Oligonucleotide analogs having modified dimers

ABSTRACT

Modified dimers having a ribose sugar moiety in the 5′ nucleoside and a 2′ modified sugar in the 3′ nucleoside are provided. The modified dimers are useful in the preparation of oligonucleotide analogs having enhanced properties compared to native oligonucleotides, including increased nuclease resistance, enhanced binding affinity and improved protein binding.

This Application is a continuation-in-part of Ser. No. 09/248,386, filedFeb. 12, 1999, which is a division of Ser. No. 08/848,840, filed Apr.30, 1997, now U.S. Pat. No. 5,965,722, which is a continuation-in-partof Ser. No. 08/468,037, filed Jun. 6, 1995, now U.S. Pat. No. 5,859,221.

FIELD OF THE INVENTION

The present invention relates to modified dimeric nucleoside compounds,oligonucleotide analogs prepared therefrom and methods of their use. Inone aspect of the present invention, oligonucleotide analogs areprovided that contain modified nucleoside dimers that enhance thehybridization of the oligonucleotide analogs to, for example, RNA. Morespecific objectives and advantages of the invention will hereinafter bemade clear or become apparent to those skilled in the art during thecourse of explanation of preferred embodiments of the invention.

BACKGROUND OF THE INVENTION

It is well known that most of the bodily states in mammals, includingmost disease states, are affected by proteins. Classical therapeuticmodes have generally focussed on interactions with such proteins in aneffort to moderate their disease-causing or disease-potentiatingfunctions. However, recently, attempts have been made to moderate theactual production of such proteins by interactions with molecules thatdirect their synthesis, such as intracellular RNA. By interfering withthe production of proteins, maximum therapeutic effect and minimal sideeffects may be realized. It is the general object of such therapeuticapproaches to interfere with or otherwise modulate gene expressionleading to undesired protein formation.

One method for inhibiting specific gene expression is the use ofoligonucleotides and oligonucleotide analogs. Certain oligonucleotideanalogs have been accepted as therapeutic agents with great promise.Oligonucleotides and oligonucleotide analogs are known to hybridize tosingle-stranded DNA or RNA molecules. Hybridization is thesequence-specific base pair hydrogen bonding of nucleobases of theoligonucleotide or the oligonucleotide analog to the nucleobases of thetarget DNA or RNA molecule. Such nucleobase pairs are said to becomplementary to one another.

In determining the extent of hybridization to a complementary nucleicacid, the relative ability of an oligonucleotide or an oligonucleotideanalog to bind to the complementary nucleic acid may be compared bydetermining the melting temperature of a particular hybridizationcomplex. The melting temperature (T_(m)), a characteristic physicalproperty of double helices, denotes the temperature (in degreescentigrade) at which 50% helical (hybridized) versus coil (unhybridized)forms are present. T_(m) is measured by using the UV spectrum todetermine the formation and breakdown (melting) of the hybridizationcomplex. Base stacking, which occurs during hybridization, isaccompanied by a reduction in UV absorption (hypochromicity).Consequently, a reduction in UV absorption indicates a higher T_(m). Thehigher the T_(m), the greater the strength of the bonds between thestrands.

For use as therapeutics, oligonucleotides and oligonucleotide analogsmust be transported across cell membranes or be taken up by cells, andappropriately hybridize to target DNA or RNA. These critical functionsdepend on the initial stability of the oligonucleotides toward nucleasedegradation. A serious deficiency of unmodified oligonucleotides whichaffects their hybridization potential with target DNA or RNA fortherapeutic purposes is the enzymatic degradation of administeredoligonucleotides by a variety of intracellular and extracellularubiquitous nucleolytic enzymes referred to as nucleases. Foroligonucleotides to be useful as therapeutics or diagnostics, theoligonucleotides should demonstrate enhanced binding affinity tocomplementary target nucleic acids, and preferably be reasonably stableto nucleases and resist degradation. For a non-cellular use such as aresearch reagent, oligonucleotides need not necessarily possess nucleasestability.

A number of chemical modifications have been introduced intooligonucleotides to increase their binding affinity to target DNA or RNAand resist nuclease degradation. The present invention describes the useof oligonucleotide analogs having modified dimers. These modified dimershave unexpectedly enhanced binding affinity when placed in anoligonucleotide.

While it has been recognized that nucleosides and oligonucleotidesbearing base and sugar modifications are useful, there remains along-felt need for oligonucleotides with greater binding affinity, henceimproved hybridization characteristics, and greater nuclease resistance.Such oligonucleotides are desired as therapeutics, diagnostics, andresearch reagents.

SUMMARY OF THE INVENTION

The present invention presents modified dimeric nucleoside compoundshaving Formula I:

wherein

Z is a covalent intersugar linkage;

each T₁ and T₂ is, independently, —OH, —OR, —CH₂R, —NH(R), —SH, —SR, ora protected hydroxyl;

B_(X) is a heterocyclic base;

X is F, O—R, S—R or N—R(R₂);

R is alkyl, or a ring system having from about 4 to about 7 carbon atomsor having from about 3 to about 6 carbon atoms and 1 or 2 hetero atomswherein said hetero atoms are selected from oxygen, nitrogen and sulfurand wherein said ring system is aliphatic, unsaturated aliphatic,aromatic or heterocyclic;

and wherein any available hydrogen atom of said ring system is eachreplaceable with an alkoxy, alkylamino, urea or alkylurea group;

or R has one of the formulas:

 wherein

Q is O, S or NR₂;

m is from 1 to 10;

y is from 0 to 10;

E is N(R₂)(R₃), N═C(R₂)(R₃), C₁-C₁₀ alkyl, or C₁-C₁₀ substituted alkylwherein said substituent is N(R₂)(R₃);

each R₂ and R₃ is, independently, H, C₁-C₁₀ alkyl, alkylthioalkyl, anitrogen protecting group, or R₂ and R₃, together, are a nitrogenprotecting group or wherein R₂ and R₃ are joined in a ring structurethat can include at least one heteroatom selected from N and O; and R₁is H or C₁-C₁₂ alkyl.

In further preferred embodiments of the compounds of the invention,oligonucleotide analogs are provided comprising at least one moietyhaving the Formula II:

wherein:

each Z is a covalent intersugar linkage;

T₃ is a nucleotide other than a ribonucleotide, a nucleoside other thana ribonucleoside, hydroxyl, a blocked hydroxyl, or an oligonucleotidewherein the 3′-terminal nucleotide of said oligonucleotide is not aribonucleotide.

T₄ is a nucleotide, a nucleoside, an oligonucleotide, a hydroxyl or ablocked hydroxyl;

with the proviso that at least one of said T₃ and T₄ is not a hydroxyl,or blocked hydroxyl;

B_(X) is a heterocyclic base;

each X is, independently, F, —O—R, —S—R, or —N—R(R₂);

R is alkyl, or a ring system having from about 4 to about 7 carbon atomsor having from about 3 to about 6 carbon atoms and 1 or 2 hetero atomswherein said hetero atoms are selected from oxygen, nitrogen and sulfurand wherein said ring system is aliphatic, unsaturated aliphatic,aromatic or heterocyclic;

and wherein any available hydrogen atom of said ring system is eachreplaceable with an alkoxy, alkylamino, urea or alkylurea group;

or R has one of the formulas:

 wherein

Q is O, S or NR₂;

m is from 1 to 10;

y is from 0 to 10;

E is N(R₂)(R₃), N═C(R₂)(R₃), C₁-C₁₀ alkyl, or C₁-C₁₀ substituted alkylwherein said substituent is N(R₂)(R₃); and

each R₂ and R₃ is, independently, H, C₁-C₁₀ alkyl, alkylthioalkyl, anitrogen protecting group, or R₂ and R₃, together, are a nitrogenprotecting group or wherein R₂ and R₃ are joined in a ring structurethat can include at least one heteroatom selected from N and O; and R₁is H or C₁-C₁₂ alkyl.

In some preferred embodiments, compounds are provided that contain atleast one moiety of Formula III:

wherein:

Z is a covalent intersugar linkage;

B_(X) is a heterocyclic base;

X is F, —O—R, —S—R or —NR(R₂);

R is alkyl, or a ring system having from about 4 to about 7 carbon atomsor having from about 3 to about 6 carbon atoms and 1 or 2 hetero atomswherein said hetero atoms are selected from oxygen, nitrogen and sulfurand wherein said ring system is aliphatic, unsaturated aliphatic,aromatic or heterocyclic;

and wherein any available hydrogen atom of said ring system is eachreplaceable with an alkoxy, alkylamino, urea or alkylurea group;

or R has one of the formulas:

 wherein

Q is O, S or NR₂;

m is from 1 to 10;

y is from 0 to 10;

E is N(R₂)(R₃), N═C(R₂)(R₃), C₁-C₁₀ alkyl, or C₁-C₁₀ substituted alkylwherein said substituent is N(R₂)(R₃);

each R₂ and R₃ is, independently, H, C₁-C₁₀ alkyl, alkylthioalkyl, anitrogen protecting group, or R₂ and R₃, together, are a nitrogenprotecting group or wherein R₂ and R₃ are joined in a ring structurethat can include at least one heteroatom selected from N and O;

T₃ is a nucleotide other than a ribonucleotide, a nucleoside other thana ribonucleoside, a hydroxyl, a blocked hydroxyl, or an oligonucleotidewherein the 3′-terminal nucleotide of said oligonucleotide is not aribonucleotide; and

R₁ is H or C₁-C₁₂ alkyl.

In some preferred embodiments, oligonucleotide analogs of the inventionare provided that contain a plurality of moieties of Formulas II or III.

In some preferred embodiments of the foregoing compounds, X is —O—R. Inother preferred embodiments X is —O—R and R is —CH₃.

In further preferred embodiments of the compounds of the invention, R is—CH₂—CH₂—O—CH₃. In still further preferred embodiments of the compoundsof the invention, Z is —N(CH₃)—O—CH₂—.

In preferred embodiments, oligonucleotide analogs of the invention areprepared to have a predetermined length. In some preferred embodiments,the length is from 1 to 200 subunits. In further preferred embodiments,the length is from 10 to 25 subunits, with from 12 to 20 subunits beingmore preferred.

DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention provides modified nucleic acid dimeric compounds(“modified dimers”), and oligonucleotides and analogs thereofincorporating such modified dimers. The oligonucleotides andoligonucleotide analogs of the present invention can contain onemodified dimer, or a plurality of modified dimers. Thus, theoligonucleotides and analogs of the invention can be essentially“nucleic acid like,” (i.e., can contain primarily unmodified nucleicacid), or can contain modified dimers at several selected positionsthroughout the oligomer. The oligonucleotide analogs of the inventioncan have a plurality of modified dimers incorporated therein in anyconfiguration.

In addition to having one or more modified dimers incorporated therein,oligonucleotide analogs of the present invention can be modified singlyor uniformly at backbone, sugar and/or base positions.

Preferred modified dimers of the invention are illustrated by Formula I:

wherein:

each Z is a covalent intersugar linkage;

each T₁ and T₂ is, independently, —OH, —OR, —CH₂R, —NH(R), —SH, —SR, ora blocked hydroxyl;

B_(X) is a heterocyclic base;

X is F, —O—R, —S—R or —NR(R₂);

R is alkyl, or a ring system having from about 4 to about 7 carbon atomsor having from about 3 to about 6 carbon atoms and 1 or 2 hetero atomswherein said hetero atoms are selected from oxygen, nitrogen and sulfurand wherein said ring system is aliphatic, unsaturated aliphatic,aromatic or heterocyclic;

and wherein any available hydrogen atom of said ring system is eachreplaceable with an alkoxy, alkylamino, urea or alkylurea group;

or R has one of the formulas:

 wherein

Q is O, S or NR₂;

m is from 1 to 10;

y is from 0 to 10;

E is N(R₂)(R₃), N═C(R₂)(R₃), C₁-C₁₀ alkyl, or C₁-C₁₀ substituted alkylwherein said substituent is N(R₂)(R₃);

each R₂ and R₃ is, independently, H, C₁-C₁₀ alkyl, alkylthioalkyl, anitrogen protecting group, or R₂ and R₃, together, are a nitrogenprotecting group or wherein R₂ and R₃ are joined in a ring structurethat can include at least one heteroatom selected from N and O; and R₁is H or C₁-C₁₂ alkyl.

In some preferred embodiments, oligonucleotides and oligonucleotideanalogs of the present invention comprise at least one moiety having theFormula III:

wherein the constituent variables are as defined above.

In the modified dimers of the present invention, the covalently linkednucleosides are joined by a covalent intersugar (backbone) linkage whichcan be a naturally-occurring phosphodiester linkage, or a non-naturallyoccurring covalent intersugar (backbone) linkage. Preferrednon-naturally occurring covalent intersugar (backbone) linkages aredescribed below.

The nucleoside comprising the 5′ end of the modified dimers of theinvention comprise a ribose sugar, and the nucleoside comprising the 3′end of the modified dimers of the invention have a 2′ modified ribosylsugar moiety.

In some preferred embodiments, one or more modified dimers of theinvention are incorporated into oligomers to form oligonucleotideanalogs of the invention. Such oligonucleotide analogs are linearpolymeric structures containing one or more modified dimers, and whichcan be attached to other monomeric or polymeric groups includingadditional modified dimers, nucleotides, nucleosides, oligonucleotidesor oligonucleosides in any combination or order. Thus, oligonucleotideanalogs of the invention are essentially covalently linked nucleosidesjoined by intersugar linkages, in which some of the adjacent nucleosidesform modified dimers of the invention. In such embodiments, it isgenerally preferred that the nucleoside or nucleotide attached directlyto the 5′-end of the modified dimer be a non-ribose nucleoside ornucleotide, such as, for example, a deoxyribonucleoside ordeoxyribonucleoside.

In some preferred embodiments, oligonucleotide analogs of the inventioncontain one or more modified dimers which can be separated by one ormore nucleotides or nucleosides. The modified dimer or modified dimerscan be present in such oligonucleotide analogs at the terminal position(i.e., at the 3′ or 5′ end of the oligonucleotide analog), or at anynumber of non-terminal positions. Thus, in some preferred embodiments ofthe compounds of the invention, oligonucleotide analogs are providedcomprising at least one moiety having the Formula II:

wherein:

each Z is a covalent intersugar linkage;

T₃ is a nucleotide other than a ribonucleotide, a nucleoside other thana ribonucleoside, a hydroxyl, a blocked hydroxyl, or an oligonucleotidewherein the 3′-terminal nucleotide of said oligonucleotide is not aribonucleotide;

T₄ is a nucleotide, a nucleoside, an oligonucleotide, a hydroxyl or ablocked hydroxyl;

with the proviso that at least one of said T₃ and T₄ is not a hydroxyl,or blocked hydroxyl;

B_(X) is a heterocyclic base;

each X is, independently, F, —O—R, —S—R, or —N—R(R₂);

R is alkyl, or a ring system having from about 4 to about 7 carbon atomsor having from about 3 to about 6 carbon atoms and 1 or 2 hetero atomswherein said hetero atoms are selected from oxygen, nitrogen and sulfurand wherein said ring system is aliphatic, unsaturated aliphatic,aromatic or heterocyclic;

and wherein any available hydrogen atom of said ring system is eachreplaceable with an alkoxy, alkylamino, urea or alkylurea group;

or R has one of the formulas:

 wherein

Q is O, S or NR₂;

m is from 1 to 10;

y is from 0 to 10;

E is N(R₂)(R₃), N═C(R₂)(R₃), C₁-C₁₀ alkyl, or C₁-C₁₀ substituted alkylwherein said substituent is N(R₂)(R₃); and

each R₂ and R₃ is, independently, H, C₁-C₁₀ alkyl, alkylthioalkyl, anitrogen protecting group, or R₂ and R₃, together, are a nitrogenprotecting group or wherein R₂ and R₃ are joined in a ring structurethat can include at least one heteroatom selected from N and O; and R₁is H or C₁-C₁₂ alkyl.

In one aspect of the present invention, the oligonucleotide analogs arefrom 1 to 200 linked nucleosides in length. A preferred length is fromabout 10 to about 25 linked nucleosides, with from about 12 to about 20linked nucleosides being more preferred.

In the context of this invention, the term “oligonucleotide” refers toan oligomer or polymer of ribonucleic acid (RNA) or deoxyribonucleicacid (DNA). The term “oligonucleotide analog” refers to oligonucleotidescomposed of nucleobases, sugars and covalent intersugar (backbone)linkages that include portions that are non-naturally-occurring. Suchmodified or substituted oligonucleotides are often preferred over nativeforms because of desirable properties such as, for example, enhancedcellular uptake, enhanced affinity for nucleic acid target and increasedstability in the presence of nucleases. A discussion of antisenseoligonucleotides and some desirable modifications can be found, forexample, in De Mesmaeker et al., Acc. Chem. Res., 1995, 28, 366,incorporated herein by reference in its entirety.

As is known in the art, a nucleoside is a “base sugar combination.” Thebase portion of the nucleoside is typically a heterocyclic base. The twomost common classes of such heterocyclic bases are the purines and thepyrimidines. Nucleotides are nucleosides that further include aphosphate group covalently linked to the sugar portion of thenucleoside. For those nucleosides that include a pentofuranosyl sugar,the phosphate group can be linked to either the 2′, 3′ or 5′ hydroxylmoieties of the sugar. In forming oligonucleotides, the phosphate groupscovalently link adjacent nucleosides to one another to form a linearpolymeric compound. In turn, the respective ends of this linearpolymeric structure can be further joined to form, for example, acircular type structure. However, open linear structures are generallypreferred.

The intersugar linkages are the groups that covalently join the sugarunits of the oligonucleotide backbone. In naturally occurringoligonucleotides, the intersugar linkages are 3′ to 5′ phosphodiesterlinkages.

Examples of preferred oligonucleotides useful in the present inventioninclude those containing modified backbones or non-natural intersugarlinkages that connect the sugar units of the oligonucleotides. As usedin this specification, oligonucleotides having modified backbonesinclude both those that retain a phosphorous atom in the backbone, andthose that do not have a phosphorous atom in the backbone. As usedherein, the terms “oligonuclectide” and “modified oligonucleotide” areintended to include nucleosides that are connected by intersugarlinkages that do not contain a phosphorous atom, and intersugar linkagesthat do contain a phosphorous atom.

In addition to phosphodiester intersugar linkages, other intersugarlinkages are useful in the present invention. Thus, preferred modifiedoligonucleotide backbones useful in the present invention include, forexample, phosphorothioates, chiral phosphorothioates,phosphorodithioates, phosphotriesters, aminoaklylphosphotriesters,methyl and other alkyl phosphonates including 3′-alkylene phosphonatesand chiral phosphonates, phosphinates, phosphoramidates including3′-amino phosphoramidate and aminoalkylphosphoramidates,thionphosphoramidates, thionalkylphosphonates,thionoalklyphosphotriesters, and boranophosphates having normal 3′-5′linkages, 2′-5′ linked analogs of these, and those having invertedpolarity wherein the adjacent pairs of nucleoside units are linked 3′-5′to 5′-3′ or 2′-5′ to 5′-2′. The various salts, mixed salts and freeacids forms of the foregoing are also preferred

Representative United States patents that teach the preparation of theabove phosphorous atom containing linkages include, but are not limitedto, U.S. Pat. Nos. 3,687,808; 4,469,863; 4,476,301; 5,023,243;5,177,196; 5,188,897; 5,264,423; 5,276,019; 5,278,302; 5,286,717;5,321,131; 5,399,676; 5,405,939; 5,453,496; 5,455,233; 5,466,677;5,476,925; 5,519,126; 5,536,821; 5,541,306; 5,550,111; 5,563,253;5,571,799; 5,587,361; 5,625,050; and 5,697,248, certain of which arecommonly owned with this application, and each of which is hereinincorporated by reference.

Preferred modified oligonucleotide backbones that do not include aphosphorous atom therein, i.e., oligonucleosides, have backbones thatare formed by short chain alkyl or cycloalkyl intersugar linkages, mixedhetero atom and alkyl or cycloalky intersugar linkages or one or more orshort chain heteroatomic or heterocyclic intersugar linkages. Theseinclude those having morpholino linkages (formed in part from the sugarportion of a nucleoside); siloxane backbones; sulfide, sulfoxide andsulfone backbones; formacetyl and thioformacetyl backbones; methyleneformacetyl and thioformacetyl backbones; alkene containing backbones;sulfamate backbones; methyleneimino and methylenehydrazino backbones;sulfonate and sulfonamide backbones; amide backbones; and others havingmixed N, O, S and CH₂ component parts.

Representative United States patents that teach the preparation of theabove “oligonucleosides” include, but are not limited to, U.S. Pat. Nos.5,034,506; 5,166,315; 5,185,444; 5,214,134; 5,216,141; 5,235,033;5,264,562; 5,264,564; 5,405,938; 5,434,257; 5,466,677; 5,470,967;5,489,677; 5,541,307; 5,561,225; 5,596,086; 5,602,240; 5,610,289;5,602,240; 5,608,046; 5,610,289; 5,618,704; 5,623,070; 5,663,312;5,633,360; 5,677,437; and 5,677,439, certain of which are commonly ownedwith this application, and each of which is herein incorporated byreference.

More preferred embodiments include oligonucleotides withphosphorothioate backbones and oligonucleosides with heteroatombackbones, and in particular —CH₂—NH—O—CH₂—, —CH₂—N(CH₃)—O—CH₂— [knownas a methylene (methylimino) or MMI backbone], —CH₂—O—N(CH₃)—CH₂—,—CH₂—N(CH₃)—N(CH₃)—CH₂— and —O—N(CH₃)—CH₂—CH₂— of the above referencedU.S. Pat. No. 5,489,677, and the amide backbones of the above referencedU.S. Pat. No. 5,602,240. Also preferred are oligonucleotides havingmorpholino backbone structures of the above referenced U.S. Pat. No.5,034,506.

Oligonucleotides may also include heterocyclic base (often referred toin the art as “nucleobase” or simply as “base”) modifications orsubstitutions. As used herein, “unmodified” or “natural” nucleobasesinclude the purine bases adenine (A) and guanine (G), and the pyrimidinebases thymine (T), cytosine (C) and uracil (U). Modified nucleobasesinclude other synthetic and natural nucleobases such as5-methylcytosine, 5-hydroxymethyl cytosine, xanthine, hypoxanthine,2-aminoadenine, 6-methyl and other alkyl derivatives of adenine andguanine, 2-propyl and other alkyl derivatives of adenine and guanine,2-thiouracil, 2-thiothymine and 2-thiocytosine, 5-halouracil andcytosine, 5-propynyl uracil and cytosine, 6-azo uracil, cytosine andthymine, 5-uracil (pseudouracil), 4-thiouracil, 8-halo, 8-amino,8-thiol, 8-thioalkyl, 8-hydroxyl and other 8-substituted adenines andguanines, 5-halo particularly 5-bromo, 5-trifluoromethyl and other5-substituted uracils and cytosines, 7-methylguanine and7-methyladenine, 8-azaguanine and 8-azaadenine, 7-deazaguanine and7-deazaadenine and 3-deazaguanine and 3-deazaadenine. Furthernucleobases include those disclosed in U.S. Pat. No. 3,687,808, thosedisclosed in the Concise Encyclopedia Of Polymer Science AndEngineering, pages 858-859, Kroschwitz, J. I., ed. John Wiley & Sons,1990, and those disclosed by Englisch et al., Angewandte Chemie,International Edition, 1991, 30, 613. Certain of these nucleobases areparticularly useful for increasing the binding affinity of theoligonucleotide analogs of the invention. These include 5-substitutedpyrimidines, 6-azapyrimidines and N-2, N-6 and O-6 substituted purines,including 2-aminopropyladenine, 5-propynyluracil and 5-propynylcytosine,5-methylcytosine substitutions have been shown to increase nucleic acidduplex stability by 0.6-1.2° C. (Sanghvi, Y. S., Crooke, S. T. andLebleu, B., eds., Antisense Research and Applications, CRC Press, BocaRaton, 1993, pp. 276-278) and are presently preferred basesubstitutions.

Representative United States patents that teach the preparation ofcertain of the above noted modified nucleobase as well as other modifiednucleobases include, but are not limited to, the above noted U.S. Pat.No. 3,687,808, as well as U.S. Pat. Nos. 4,845,205; 5,130,302;5,134,066; 5,175,273; 5,367,066; 5,432,272; 5,457,187; 5,459,255;5,484,908; 5,502,177; 5,525,711; 5,552,540; 5,587,469; 5,594,121;5,596,091; 5,614,617; and 5,681,941, certain of which are commonlyowned, and each of which is herein incorporated by reference, andcommonly owned and allowed U.S. patent application Ser. No. 08/762,588,filed Dec. 10, 1996, also herein incorporated by reference.

Other preferred antisense compounds of the invention are formed ascomposite structures of at least one modified dimer and one or moreoligonucleotides, modified oligonucleotides and or oligonucleosides asdescribed above, or oligonucleotide mimetics. Such compounds have beenreferred to in the art as hybrids or “gapmers.” Representative UnitedStates patents that teach the preparation of such hybrid structuresinclude, but are not limited to, U.S. Pat. Nos. 5,013,830; 5,149,797;5,220,007; 5,256,775; 5,366,878; 5,403,711; 5,491,133; 5,565,350;5,623,065; 5,652,355; 5,652,356; and 5,700,922, certain of which arecommonly owned, and each of which is herein incorporated by reference,and commonly owned and allowed U.S. patent application Ser. No.08/465,880, filed Jun. 6, 1995, also herein incorporated by reference.

Representative sugar modifications that are amenable to the presentinvention include 2′ modifications such as OH, F, O—, S—, or N-alkyl,O—, S—, or N-alkenyl, or O, S- or N-alkynyl, wherein the alkyl, alkenyland alkynyl are substituted or unsubstituted C₁ to C₁₀ alkyl or C₂ toC₁₀ alkenyl and alkynyl, particularly O[(CH₂)_(n)O]_(m)OCH₃,O(CH₂)_(n)OCH₃, O(CH₂)_(n)NH₂ or O(CH₂)_(n)CH₃ where n and m are from 1to about 10. Other 2′ modifications include C₁ to C₁₀ lower alkyl;substituted lower alkyl, alkaryl, araalkyl, O-alkaryl or O-aralkyl, SH,SCH₃, OCN, Cl, Br, CN, CF₃, OCF₃, SOCH₃, SO₂CH₃, ONO₂, NO₂, N₃, NH₂,heterocycloalkyl, heterocycloalkaryl, aminoalkylamino, polyalkylamino,substituted silyl, an RNA cleaving group, a reporter group, anintercalator, a group for improving the pharmacokinetic properties of anoligonucleotide, or a group for improving the pharmacodynamic propertiesof an oligonucleotide, and other substituents having similar properties.A preferred modification includes 2′-methoxyethoxy, i.e., analkoxyalkoxy group (2′-O—CH₂CH₂OCH₃, also known as2′-O-(2-methoxyethyl)) (Martin et al., Helv. Chim. Acta, 1995, 78, 486).Other preferred modifications include 2′-methoxy (2′-O—CH₃),2′-aminopropoxy (2′-OCH₂CH₂CH₂NH₂) and 2′-fluoro (2′-F).

Further preferred sugar substituents include those disclosed in U.S.application entitled “RNA Targeted 2′-modified Oligonucleotides That AreConformationally Preorganized” filed Jul. 27, 1998; U.S. Applicationentitled “Aminooxy-modified Oligonucleotides” filed Jan. 30, 1998; U.S.application entitled “Aminooxy-modified Oligonucleotides And Methods ForMaking Same” filed Aug. 7, 1998; and U.S. application entitled“2′-o-dimethylaminoethyloxyethyl-modified Oligonucleotides”, filedconcurrently with the present application. Each of the foregoingapplications is commonly owned by the assignee of the presentapplication. The contents of each of the foregoing applications arehereby incorporated by reference in their entirety.

In further preferred embodiments of the present invention,oligonucleotides of the invention can be chemically linked to one ormore moieties or conjugates which enhance the activity, cellulardistribution or cellular uptake of the oligonucleotide. Such moietiesinclude but are not limited to lipid moieties such as a cholesterolmoiety (Letsinger et al., Proc. Natl. Acad. Sci. USA, 1989, 86, 6553),cholic acid (Manoharan et al., Bioorg. Med. Chem. Let., 1994, 4, 1053),a thioether, e.g., hexyl-S-tritylthiol (Manoharan et al., Ann. N.Y.Acad. Sci., 1992, 660, 306; Manoharan et al., Bioorg. Med. Chem. Let.,1993, 3, 2765), a thiocholesterol (Oberhauser et al., Nucl. Acids Res.,1992, 20, 533), an aliphatic chain, e.g., dodecandiol or undecylresidues (Saison-Behmoaras et al., EMBO J., 1991, 10, 111; Kabanov etal., FEBS Lett., 1990, 259, 327; Svinarchuk et al., Biochimie, 1993, 75,49), a phospholipid, e.g., di-hexadecyl-rac-glycerol or triethylammonium1,2-di-O-hexadecyl-rac-glycero-3-H-phosphonate (Manoharan et al.,Tetrahedron Lett., 1995, 36, 3651; Shea et al., Nucl. Acids Res., 1990,18, 3777), a polyamine or a polyethylene glycol chain (Manoharan et al.,Nucleosides & Nucleotides, 1995, 14, 969), or adamantane acetic acid(Manoharan et al., Tetrahedron Lett., 1995, 36, 3651), a palmityl moiety(Mishra et al., Biochim. Biophys. Acta, 1995, 1264, 229), or anoctadecylamine or hexylamino-carbonyl-oxycholesterol moiety (Crooke etal., J. Pharmacol. Exp. Ther., 1996, 277, 923), all references beingincorporated herein by reference.

Representative United States patents that teach the preparation of sucholigonucleotide conjugates include, but are not limited to, U.S. Pat.Nos. 4,828,979; 4,948,882; 5,218,105; 5,525,465; 5,541,313; 5,545,730;5,552,538; 5,578,717, 5,580,731; 5,580,731; 5,591,584; 5,109,124;5,118,802; 5,138,045; 5,414,077; 5,486,603; 5,512,439; 5,578,718;5,608,046; 4,587,044; 4,605,735; 4,667,025; 4,762,779; 4,789,737;4,824,941; 4,835,263; 4,876,335; 4,904,582; 4,958,013; 5,082,830;5,112,963; 5,214,136; 5,082,830; 5,112,963; 5,214,136; 5,245,022;5,254,469; 5,258,506; 5,262,536; 5,272,250; 5,292,873; 5,317,098;5,371,241, 5,391,723; 5,416,203, 5,451,463; 5,510,475; 5,512,667;5,514,785; 5,565,552; 5,567,810; 5,574,142; 5,585,481; 5,587,371;5,595,726; 5,597,696; 5,599,923; 5,599,928 and 5,688,941, certain ofwhich are commonly owned, and each of which is herein incorporated byreference.

Oligonucleotides of the invention may also be admixed, encapsulate,conjugated or otherwise associated with other molecules, moleculestructures or mixtures of compounds, as for example, liposomes, receptortargeted molecules, oral, rectal, topical or other formulations, forassisting in uptake, distribution and/or absorption. RepresentativeUnited States patents that teach the preparation of such uptake,distribution and/or absorption assisting formulations include, but arenot limited to, U.S. Pat. Nos. 5,108,921; 5,354,844; 5,416,016;5,459,127; 5,521,291; 5,543,158; 5,547,932; 5,583,020; 5,591,721;4,426,330; 4,534,899; 5,013,556; 5,108,921; 5,213,804; 5,227,170;5,264,221; 5,356,633; 5,395,619; 5,416,016; 5,417,978; 5,462,854;5,469,854; 5,512,295; 5,527,528; 5,534,259; 5,543,152; 5,556,948;5,580,575; and 5,595,756, each of which is herein incorporated byreference.

The oligonucleotides of the invention may be provided as prodrugs, whichcomprise one or more moieties which are cleaved off, generally in thebody, to yield an active oligonucleotide. One example of a prodrugapproach is described by Imbach et al. in WO Publication 94/26764,incorporated herein by reference.

As used herein, the term “alkyl” includes but is not limited to straightchain and branch chain saturated hydrocarbon groups including but notlimited to methyl, ethyl, and isopropyl groups. Alkyl groups of thepresent invention may be substituted. Representative alkyl substituentsare disclosed in U.S. Pat. No. 5,212,295, at column 12, lines 41-50,hereby incorporated by reference in its entirety. The term cycloalkyl isintended to denote a cyclic alkyl group.

Alkenyl groups according to the invention are to straight chain, branchchain, and cyclic hydrocarbon groups containing at least onecarbon-carbon double bond, and alkynyl groups are to straight chain,branch chain, and cyclic hydrocarbon groups containing at least onecarbon-carbon triply bond. Alkenyl and alkynyl groups of the presentinvention can be substituted.

Aryl groups are substituted and unsubstituted aromatic cyclic moietiesincluding but not limited to phenyl, naphthyl, anthracyl, phenanthryl,pyrenyl, and xylyl groups. Alkaryl groups are those in which an arylmoiety links an alkyl moiety to a core structure, and aralkyl groups arethose in which an alkyl moiety links an aryl moiety to a core structure.

In general, the term “hetero” denotes an atom other than carbon,preferably but not exclusively N, O, or S. Accordingly, the terms“heterocycloalkyl” and “heteroaryl” denote, respectively, a cycloalklylor aryl moiety containing at least one heteroatom (i.e., non-carbonatom).

The term alkoxy denotes a group of formula —O-alkyl. The term“alkylamino” is intended to mean a group of formula —NH(R′) or—N(R′)(R″) wherein R′ and R″ are each alkyl.

A number of chemical functional groups can be introduced into compoundsof the invention in a blocked form and subsequently deblocked to form afinal, desired compound. In general, a blocking group renders a chemicalfunctionality of a molecule inert to specific reaction conditions andcan later be removed from such functionality without substantiallydamaging the remainder of the molecule (Green and Wuts, ProtectiveGroups in Organic Synthesis, 2d edition, John Wiley & Sons, New York,1991). For example, amino groups can be blocked as phthalimido groups,as 9-fluorenylmethoxycarbonyl (FMOC) groups, and withtriphenylmethylsulfenyl, t-BOC or benzyl groups. Carboxyl groups can beprotected as acetyl groups. Representative hydroxyl protecting groupsare described by Beaucage et al., Tetrahedron 1992, 48, 2223. Preferredhydroxyl protecting groups are acid-labile, such as the trityl,monomethoxytrityl, dimethoxytrityl, trimethoxytrityl,9-phenylxanthine-9-yl (Pixyl) and 9-(p-methoxyphenyl)xanthine-9-yl(MOX). Chemical functional groups can also be “blocked” by includingthem in a precursor form. Thus, an azido group can be used considered asa “blocked” form of an amine, because the azido group is easilyconverted to the amine.

In one embodiment oligonucleotide analogs of the invention are comprisedof a plurality of modified dimers. When two or more modified dimers ofthe invention are present in an oligonucleotide analog of the invention,they may be located adjacent to one another, or they may be separated byone or more covalently linked nucleosidic subunits. In some preferredembodiments wherein three or more modified dimers are present in anoligonucleotide analog of the invention, the modified dimers may belinked, (i.e., be adjacent to one another) separated by one or morenucleosidic subunits, or some may be linked and some may be separated.All such configurations are within the present invention.

The incorporation of 2′-hydroxyl groups on the 5′-nucleoside of modifieddimers of the invention has been shown to stabilize the C-3 endo sugarpucker which is necessary for target RNA binding. A 2′-hydroxyl group isalso able to form an intramolecular hydrogen bond with a sugar O-4 ringatom on the 3′ side which leads to intra strand axial stabilization. A2′-hydroxyl group is also a recognition element in the interactionsbetween proteins and RNA. 2′-Hydroxyl groups act as both donors andacceptors in a variety of intramolecular and intermolecular hydrogenbonding interactions that stabilize secondary structural motifs of RNAor RNA mimics providing a basis for polymorphic structure. 2′-Hydroxylgroups contribute to structure stabilization through bound watermolecules and can function as ligands for coordinating metal cationswhich are involved in a wide variety of biological functions.

It has been surprisingly discovered that the oligonucleotide analogs ofthe present invention show enhanced affinity for complementary RNA. Thisenhanced affinity is illustrated in the examples below. Additionalobjects, advantages, and novel features of this invention will becomeapparent to those skilled in the art upon examination of the followingexamples thereof, which are intended to be illustrative and not intendedto be limiting.

EXAMPLE 1 5-O-TIPS-1,2-O-isopropylidene-a-D-xylofuranose

A mixture of 1,2-O-isopropylidene-D-xylofuranose (Sigma ChemicalCompany) (8.96 g, 47 mmol) in dry DMF (100 mL), TIPSCl (10.0 g, 52mmol), Et₃N (13 mL, 94 mmol) and DMAP (0.47 g, 3.9 mmol) was stirredovernight at rt then diluted with hexanes (500 mL) washed with water(4×100 mL), 0.05 N aqueous HCl (2×50 mL) water (100 mL), brine (100 mL)and dried over MgSO₄. The evaporated residue was purified on a shortsilica gel column with hexanes-EtOAc (12:1 and 4:1) to give 15.6 g (95%)of the title compound as a colorless oil. ¹H-NMR (CDCl₃): d 1.03 (m,21H, 3Pr^(i)), 1.27, 1.44 (2s, 6H, CMe₂), 4.06-4.24 (2m, 3H, H-4, H-5a,H-5b), 4.30 (d, 1H, H-3; J_(3,4)=2.6 Hz), 4.47 (d, 1H, H-2; J_(1,2)=3.7Hz), 5.92 (d, 1H, H-1), 4.36-4.52 (br, 1H, OH). ¹³C-NMR (CDCl₃): d11.57, 12.22 (3CHMe ₂), 17.60, 17.84, 17.88 (3 CHMe₂), 26.03, 26.69 (CMe₂), 62.59 (C-5), 76.76 (C-3), 78.29 (C-2), 85.44 (C-4), 104.85 (C-1),111.31 (CMe₂). CI MS (NH₃): 347 (MH⁺); EI MS: m/z=331.19406 (M⁺-15);C₁₆H₃₁O₅Si requires 331.19440.

EXAMPLE 2 3-Keto-5-O-TIPS-1,2-O-isopropylidene-a-D-xylose

5-O-TIPS-1,2-O-isopropylidene-a-D-xylose was oxidized following theprocedure of Moffat using Ac₂O in DMSO. After workup and purification byvacuum distillation a 78% yield of the title compound was isolated.

The NMR spectra was consistent with the structure.

EXAMPLE 35-O-TIPS-3-deoxy-3-didehydro-3-[2-(1,3-dithianylidene)]-1,2-O-isopropylidene-a-D-ribofuranose

To a solution of 2-(trimethylsilyl)-1,3-dithiane (prepared according tothe procedure by Seebach, et al., Chem. Ber, 1973, 106, 2277) (384 mg, 2mmol) in THF (4 mL) at −78° C. under argon was added dropwise 1.6 M BuLiin n-hexane (1.25 mL, 2 mmol). The mixture was allowed to warm to 0° C.in 3 hours and stirred at room temperature for 10 minutes and thencooled again to −78° C. 3-Keto-5-O-TIPS-1,2-O-isopropylidene-a-D-xylose(2 mmol, previously dried for overnight at rt over P₂O₅, under reducedpressure) in THF (4 mL) was added dropwise into the yellow solution ofLidithiane. The mixture was gradually warmed to room temperature duringan overnight stirring, then poured into water (30 mL) and extracted withCH₂Cl₂ (2×30 mL). The combined CH₂Cl₂ extracts were washed with water(5×10 mL), dried (MgSO₄) and evaporated to give 0.67 g of the crudetitle compound as a yellow oil. Purification was accomplished by elutionover a silica gel column (2×30 cm) with EtCAc-hexanes (1:7) to give a60% yield of the title compound as a colorless oil.

¹H-NMR (CDCl₃): d 1.03 (m, 21H, 3Pr^(i)), 1.41 (s, 6H, CMe₂), 2.12 (m,2H, H-5′a,b), 2.76-3.06 (m, 4H, H-4′a,e, H-6′a,e), 3.76 (dd, 1H, H-5a;J_(5a,5b)=10.4, J_(5a,4)=1.9 Hz), 3.88 (dd, 1H, H-5b; J_(5b,4)=1.8 Hz),4.91 (m, 1H, H-4′), 5.14 (dd, 1H, H-2; J_(2,4)=1.4, J_(1,2)=4.5 Hz),5.97 (d, 1H, H-1). ¹³C-NMR (CDCl₃): d 11.86 (3CHMe ₂), 17.91 (3CHMe₂),24.10 (C-5′) 27.43, 27.77 (CMe ₂), 28.33, 28.77 (C-4′,C-6′), 65.60(C-5), 82.30, 82.84 (C-2, C-4), 105.81 (C-1), 112.54 (CMe₂), 127.74(C-3), 136.05 (C-2′). EI MS: m/z 446.20016 (M⁺); C₂₁H₃₈O₄S₂Si requires446.20039.

EXAMPLE 43-Deoxy-3-didehydro-3-[2-(1,3-dithianylidene)]-1,2-O-isopropylidene-α-D-ribofuranose

Into an ice-cold solution of5-O-TIPS-3-deoxy-3-didehydro-3-[2-(1,3-dithianylidene)]-1,2-O-isopropylidene-α-D-ribofuranose(7.7 g, 17 mmol) in THF (150 mL) was quickly added 1M TBAF in THF (34mL, 34 mmol). The mixture was left stirring in an ice bath for ½ hourand then the reaction quenched with water (10 mL) and concentrated. Theresidue was dissolved in EtOAc (750 mL), washed with water (8×100 mL)and brine (150 mL), dried (MgSO₄) and evaporated. The oily residuesolidified after being kept in high vacuum overnight. Treatment withhexanes gave 4.2 g (85%) of the title compound in high purity (mp 101-4°C. (from hexanes-EtOAc).

¹H-NMR (CDCl₃): d 1.22, 1.25 (2s, 6H, CMe₂), 1.61 (apparent t, 1H,5-OH), 1.97 (m, 2H, H-5′a,e), 2.64, 2.91 (2m, 4H, H-4′a,e, H-6′a,e),3.51 (td, 1H, H-5a; J_(5a,5b)=11.7, J_(5a,4)=J_(5a,5-OH)=4.9 Hz), 3.60(ddd, 1H, H-5b; J_(5b,4)=2.9, J_(5b,5-OH)=7.3 Hz), 4.74 (m, 1H, H-4),5.02 (dd, 1H, H-2; J_(1,2)=4.4, J_(2,4)=1.9 Hz), 5.74 (d, 1H, H-1).¹³C-NMR (CDCl₃): d 23.41 (C-5′), 27.13, 27.40 (CMe ₂), 27.77, 28.19(C-4′, C-6′), 62.83 (C-5), 81.14 (C-2), 82.78 (C-4), 104.51 (C-1),111.33 (CMe ₂), 127.77 (C-3), 135.16 (C-2′). EI MS: m/z 290.,06500 (M⁺);C₁₂H₁₈O₄S₂ requires 290.06464.

EXAMPLE 53-Deoxy-3-[2-(1,3-dithianyl)]-1,2-O-isopropylidene-a-D-ribofuranose

A solution of3-deoxy-3-didehydro-3-[2-(1,3-dithianylidene)]-1,2-O-isopropylidene-α-D-ribofuranose(3.33 g, 11.5 mmol) in dry THF (40 mL) was added slowly into a wellstirred suspension of LiAlH₄ (1.6 g, 43 mmol) in dry THF (100 mL) underargon. The mixture was stirred at 55° C. for 6 hours and then cooled inan ice bath. Successive dropwise additions of water (1.6 mL), 15%aqueous NaOH (1.6 mL) and water (4.8 mL) was followed by stirring atroom temperature for 45 minutes. The mixture was filtered by suction andthe filter cake washed with EtOAc (700 mL). The filtrate was evaporatedand the residue partitioned between EtOAc (500 mL) and water (100 mL).The organic layer was washed with water (2×75 mL), saturated aqueousNaHCO₃ (75 mL), water (75 mL) and dried (MgSO₄). Evaporation of thesolvent yielded 2.67 g (80%) of the title compound in high purity.

¹H-NMR (CDCl₃): d 1.33, 1.52 (2s, 6H, CMe₂), 1.91-2.01 (m, 2H, H-5′a,5-OH), 2.01-2.09 (m, 1H, H-5′-e), 2.60-2.70 (m, 1H, H-3), 2.74-2.95 (3m,4H, H-4′a,e, H-6′a,e), 3.92 (ddd, 1H, H-5a; J_(5a,5b)=12.2,J_(5a,4)=3.3, J_(5a,5-OH)=8.8 Hz), 4.01 (ddd, 1H, H-5b; J_(5b,4)=2.2,J_(5b,5-OH)=4.7 Hz), 4.12 (td, 1H, H-4; J_(4,3)=9.8 Hz), 4.19 (d, 1H,H-2′; J_(2′,3)=10.7 Hz), 4.81 (t, 1H, H-2; J_(1,2)=J_(2,3)=3.9 Hz), 5.76(d, 1H, H-1). ¹³C-NMR (CDCl₃): d 24.93 (C-5′), 26.01, 26.39 (CMe ₂),27.73, 28.25 (C-4′,C-6′), 41.75 (C-3), 62.51 (C-5), 80.64 (C-2), 81.44(C-4), 103.23 (C-1), 111.64 (CMe₂). EI MS: m/z 292.08029 (M⁺);C₁₂H₂₁O₄S₂ requires 292.08050.

EXAMPLE 65-O-TBDPS-3-deoxy-3-[2-(1,3-dithianyl)]-1,2-O-isopropylidene-a-D-ribofuranose

To a solution of3-deoxy-3-[2-(1,3-dithianyl)]-1,2-O-isopropylidene-a-D-ribofuranose(2.53 g, 8.7 mmol) in DMF (30 mL) and imidazole (1.18 g, 17.4 mmol) wasadded TBDPSCl (2.26 mL, 8.7 mmol). After stirring for 2 hours at roomtemperature the mixture was poured into water (1 L) and extracted withEtOAc (2×300 mL). The combined organic extracts were washed with water(5×150 mL), dried (MgSO₄) and evaporated to give 4.6 g (100%) of thetitle compound as a colorless oil which was used for acetolysis withoutany further purification.

¹H-NMR (CDCl₃): d 1.06 (s, 9H, Bu), 1.37, 1.52 (CMe₂), 2.01 (m, 2H,H-5′a,e), 2.69 (m, 1H, H-3), 2.80-3.06 (m, 4H, H-4′a,e, H-6′a,e), 4.05(d, 2H, H-5a, H-5b; J_(5a,4)=J_(5b,4)=2.0 Hz), 4.14 (m, 2H, H-4, H-2′),4.84 (apparent t, 1H, H-2), 5.80 (d, 1H, H-1; J_(1,2)=3.6 Hz),7.34-7.40, 7.61-7.72 (2d, 10H, 2Ph). EI MS: m/z 473.13310 (M⁺-57)C₂₄H₂₉O₄S₂Si requires 473.13332.

EXAMPLE 75-O-TBDPS-3-deoxy-3-[2-(1,3-dithianyl)]-1,2-di-O-acetyl-β-D-ribofuranose

To a solution of5-O-TBDPS-3-deoxy-3-[2-(1,3-dithianyl)]-1,2-O-isopropylidene-a-D-ribofuranose(4.13 g, 7.8 mmol) in AcOH (119 mL) and Ac₂O (19 mL) at 75° C. was addedCSA (5.45 g, 23.4 mmol) with stirring at 75° C. for 15 minutes. Themixture was cooled in an ice bath and poured into aqueous Na₂CO₃ (216 gin 1.38 L water). After stirring for ½ hour at room temperature themixture was extracted with EtOAc (3×400 mL). The combined extracts werewashed with saturated aqueous NaHCO₃ (3×200 mL) and water (300 mL),dried (MgSO₄) and evaporated to give a mixture of the title compound andthe open chain 1-O-acetyl-1,2-O-isopropylidene sugar as a pale brownfoam (4.4 g; 85% of the title compound was present in the mixture asdetermined from ¹H-NMR). The mixture was separated on silica gel column(4.5×44 cm) with EtOAc-hexanes (1:12 and 1:6) to give 3.05 g (70%) ofthe title compound as a colorless foam.

The title compound: ¹H-NMR (CDCl₃): d 1.06 (s, 9H, CMe₃), 1.76, 2.10(2s, 6H, 2OAc), 1.95 and 2.15-2.30 (2m, 2H, H-5′a,e), 2.62-3.0 (m, 4H,H-4′a,e, H-6′a,e), 3.21 (dt, 1H, H-3; J_(3,2)=J_(3,4)=4.7, J_(3,2′)=9.7Hz), 3.93 (dd, 1H, H-5a; J_(5a,4)=3.9, J_(5a,5b)=11.5 Hz), 4.03-4.12(2m, 2H, H-2′, H-5b), 4.32 (ddd, 1H, H-4; J_(4,5)=1.7 Hz), 5.35 (d, 1H,H-2), 6.07 (s, 1H, H-1), 7.38, 7.69 (2m, 9H, 6H, 2Ph). ¹³C-NMR (CDCl₃):d 19.35 (CMe₃), 20.84, 20.95 (2COMe), 25.45 (C-5′), 26.66, 26.86 (CMe₃), 28.76, 29.02 (C-4′,C-6′), 42.54, 43.01 (C-3, C-2′), 65.34 (C-5),77.53 (C-2), 84.79 (C-4), 98.10 (C-1), 127.64, 127.69, 129.59, 129.79,135.45, 135.58 (3Ph), 169.42, 169.61 (2COMe). EI MS: m/z 517.11747(M⁺-57) C₂₅H₂₉O₆S₂Si requires 517.11700.

EXAMPLE 85-Methyl-2′-O-acetyl-5′-O-TBDPS-3′-deoxy-3′-[2-(1,3-dithianyl)]uridine

Prior to the preparation of the title compound a stock solution ofbis(trimethylsilyl)thymine was prepared following the general procedureof Vorbrrueggen, et al., Chem. Ber. 1981, 114, 1234. A mixture ofthymine (3.3 g, 30 mmol), HMDS (55 mL) and pyridine (22 mL) was stirredovernight at reflux and then distilled. At first the pressure ofdistillation was maintained at atmospheric and after all fractions hadcome over the distillation was continued at reduced pressure. Thebis(trimethylsilyl)thymine was collected at 0.21 Torr with a boilingpoint of 99-100° C. This material slowly solidified after being storedin a dessicator.

A solution of5-O-TBDPS-3-deoxy-3-[2-(1,3-di-thianyl)]-1,2-di-O-acetyl-β-D-ribofuranose(2.62 g, 4.6 mmol) in dry 1,2-dichloroethane (80 mL),bis(trimethylsilyl)thymine (1.36 mL, 5.0 mmol) and TMS-triflate (0.83mL, 4.6 mmol) was stirred for ½ hour at reflux temperature under argon.The reaction mixture was cooled in an ice bath, poured into 5% aqueousNaHCO₃ (380 mL) and extracted three times with CH₂Cl₂ (400 mL, 2×150mL). The combined extracts were washed with water (4×200 mL), dried(MgSO₄) and evaporated to give 3.0 g (100%) of the title compound as apale yellow foam.

¹H-NMR (CDCl₃): d 1.10 (s, 9H, CMe₃), 1.49 (d, 3H, C5-Me, J_(Me,H-6)=0.9Hz), 1.74-1.92 (m, 2H, H-2Óa,e), 2.14 (s, 3H, COMe), 2.68-2.92 (m, 5H,H-3′, H-4Óa,e, H-6Óa,e), 3.96 (dd, 1H, H-5′a; J_(5′a,5′b)=11.9,J_(5′a,4)=2.5 Hz), 4.14 (d, 1H, H-2Ó; J_(2Ó,3′)=6.3 Hz), 4.18 (dd, 1H,H-5′b; J_(5′b,4)=1.4 Hz), 4.38 (md, 1H, H-4′, J_(4′,3′)=7.8 Hz), 5.52(dd, 1H, H-2′; J_(2′,1′)=3.9, J_(2′,3′)=7.3 Hz), 7.31-7.41, 7.63-7.71(2m, 10H, 7H, 2Ph, H-6), 8.79 (s, 1H, NH). ¹³C-NMR (CDCl₃) d 11.85(C5-Me), 19.45 (CMe₃), 20.95 (COMe), 25.37 (C-5Ó), 27.08 (CMe ₃), 29.57,30.18 (C-4Ó,C-6Ó), 43.85 (C-3′), 44.17 (C-2Ó), 64.53 (C-5′), 76.41(C-2′), 81.99 (C-4′), 88.26 (C-1′), 111.39 (C-5), 127.83, 127.86,129.90, 129.98, 132.56, 133.10, 8135.34, 135.57 (2Ph), 135.25 (C-6),150.09 (C-4), 163.45 (C-2), 169.68 (COMe). FAB MS: m/z 641 (MH⁺); EI MSm/z 583.13902 (M⁺-57), C₂₈H₃₁N₂O₆S₂Si requires 583.13950.

EXAMPLE 95-Methyl-5′-O-tert-butyldiphenysilyl-3′-deoxy-3′-[2-(1,3-dithianyl)]uridine

To a mixture of5-methyl-2′-O-acetyl-5′-O-TBDPS-3′-deoxy-3′-[2-(1,3-dithianyl)]uridine(3.2 g, 4.5 mmol) in MeOH (150 mL), was added dropwise 0.1 N aqueousNaOH (30 mL). After stirring overnight at room temperature 5 mL of 0.1 Naqueous NaOH was added and stirring continued for 8 hours. The mixturewas neutralized by dropwise addition of 15% aqueous AcOH, diluted withMeOH (100 mL) and water (100 5 mL) and concentrated. The residue waspartitioned between CH₂Cl₂ (750 mL) and water (400 mL). The aqueouslayer was extracted with CH₂Cl₂ (2×200 mL) and the combined extractswashed with water (3×200 mL), dried (MgSO₄) and evaporated to give 2.54g (95%) of the title compound in high purity as a pale yellow foam.

¹H-NMR (CDCl₃, 499.8 MHZ): d 1.12 (s, 9H, (CMe₃), 1.35 (d, 3H, C5-Me;J_(Me,H-6)=0.7 Hz), 1.84-1.94 (m 1H, H-5Óa) 2.03-2.11 (m, 1H, H-5Óe),2.70 (dt, 1H, H-3′; J_(3′,2′)=5.5, J_(3′,2Ó)=J_(3′,4′)=8.9 Hz), 2.83 (m,2H, H-4Ó,e), 2.85, 2.91 (2m, 2H, H-6Óa,e), 4.14 (dd, 1H, H-5′a;J_(5′a,5)′b=12.0, J_(5′a,4′)=2.8 Hz), 4.32 (dd, 1H, H-5′b;J_(5′b,4′)=1.0 Hz), 4.44 (md, 1H, H-4′), 4.52 (dd, 1H, H-2′;J_(2′,3′)=5.4, J_(1′,2′)=1.5 Hz), 5.84 (d, 1H, H-1′), 7.38, 7.42, 7.68,7.73 (4m, 10H, 2Ph), 7.64 (q, 1H, H-6). ¹³C NMR (CDCl₃) d 11.76(C-5-Me), 19.56 (CMe₃), 25.50 (C-5Ó), 27.19 (2CMe ₃), 30.16, 30.64(C-4′, C-6Ó), 44.41, 44.64 (C-2Ó, C-3′), 64.43 (C-5′), 77.38 (C-2′),83.24 (C-4′), 91.53 (C-1′), 110.65 (C-5), 127.72, 127.85, 129.90,129.98, 132.76, 133.37, 135.29, 135.59 (2Ph), 135.10 (C-6), 150.69(C-4), 163.91 (C-2). FAB MS: m/z 599 (MH⁺); EI MS m/z 541.12871 (M⁺-57);C₂₆H₂₉N₂O₅S₂Si requires 541.12810.

EXAMPLE 10 5-Methyl-5′-O-TBDPS-3′-deoxy-3′-C-formyluridine

A mixture of5-methyl-5′-O-tert-butyldiphenysilyl-3′-deoxy-3′-[2-(1,3-dithianyl)]uridine(2.44 g, 4.1 mmol) in degassed water-acetone (1:9, v/v; 200 mL), HgCl₂(3.32 g, 12.3 mmol) and yellow HgO (2.65 g, 12.3 mmol) was vigorouslystirred at reflux temperature for 12 hours. The reaction mixture wasfiltered through a celite pad which was thoroughly washed with CH₂Cl₂(600 mL). The combined solutions were washed with 25% aqueous ammoniumacetate (5×200 mL) and brine (300 mL), dried over Na₂SO₄ in an ice coldbath and evaporated to give 1.93 g (94%) of the title compound as awhite solid (mp 132-8° C. (decomposition). This material was useddirectly for further coupling.

¹H NMR (CDCl₃) d 1.06 (s, 9H, CMe₃), 1.46 (d, 3H, C5-Me;J_(Me,H-6)=0.8Hz), 1.9 (br, 1H, OH), 3.30 (dd, 1H, H-3′; J_(3′4′)=9-4,J_(3′2′)=5.7 Hz), 3.95 (dd, 1H, H-5′a; J_(5′a,5′b)=12.2, J_(5′a,4′)=2.4Hz), 4.26 (dd, 1H, H-5′b; J_(5′b,4′)=1.8 Hz), 4.79 (apparent td, 1H,H-4′), 4.90 (d, 1H, H-2′), 5.75 (s, 1H, H-1′), 7.33-7.44 and 7.59-7.65(2m, 6H, 4H, 2Ph), 7.67 (q, 1H, H-6), 9.83 (s, 1H, CHO), 10.24 (s, 1H,NH). ¹³C NMR (CDCl₃): d 12.00 (C5-Me), 19.45 (CMe₃), 27.03 (2CMe ₃),52.63 (C-3′), 63.11 (C-5′), 77.31 (C-2′), 80.90 (C-4′), 93.26 (C-1′),110.75 (C-5), 127.95, 128.04, 130.07, 130.17, 132.26, 133.04, 135.18,135.44 (2Ph,C-6), 150.84 (C-4), 164.43 (C-2), 197.81 (CHO). FAB MS: m/z509 (MH⁺); C₂₇H₃₃N₂O₆Si requires 509.20559.

EXAMPLE 11 3′-O-TBDPS-2′-O-methyl-5′-O-(N-methylamino)-5-methyluridine

To a solution of3′-O-TBDPS-2′-O-methyl-5′-O-(methyleneimino)-5-methyluridine (preparedas per the procedure illustrated in Bhat et al., J. Org. Chem., 1996,61, 8186-8199) (8.02 g, 15.0 mmol) in acetic acid (75 mL) was cooled inan ice bath to 10° C. After 5 minutes at this temperature NaBH₃CN (1.0g, 15.9 mmol) was added in one portion and the stirring continued atthis temperature for minutes. The bath was removed, the suspensionallowed to warm to room temperature over 30 minutes. The reactionmixture was stirred at this temperature for an additional 30 minutes. Itwas then concentrated to a smaller volume (50 mL) under reduced pressureand poured into ice cold water (500 mL) and extracted in CH₂Cl₂ (3×120mL), washed with water (2×50 mL) followed by aqueous NaHCO₃ solution(2×100 mL). The organic layer was then washed with brine (100 mL) anddried over anhydrous Na₂SO₄. The solvent was removed under reducedpressure and the product was purified by silica gel flash columnchromatography using EtOAc:hexane (60/40, v/v) as the eluent. Theappropriate fractions were combined and concentrated to give 7.0 g (87%)of the title compound.

R_(f) 0.52 (EtOAc:hexane, 80/20, v/v). ¹H NMR (CDCl₃) δ 8.48 (bs, 1H),7.70-7.30 (m, 11H), 5.91 (d, J=2.5 Hz, 1H), 5.36 (bs, 1H), 4.23-4.06 (m,2H), 3.98 (dd, 1H), 3.63 (dd, 1H), 3.35 (s, 3H), 3.22 (m, 1H), 2.63 (s,3H), 1.83 (s, 3H), 1.10 s, (9H). HRMS (FAB⁺, NBA/NaI) calcd forC₂₈H₃₇N₃O₆Si+Na⁺ 562.2349, found 562.2336.

EXAMPLE 123′-De(oxyphosphinico)-3′-methylene(methylimino)-5′-O-TBDPS-5-methyluridinyl-(3>5)-3′-O-TBDPS-2′-O-methyl-5-methyluridine

To an ice-cold solution of5-methyl-5′-O-TBDPS-3′-deoxy-3′-C-formyluridine (1.36 g, 2.68 mmol) and3′-O-TBDPS-2′-O-methyl-5′-O-(N-methylamino)-5-methyluridine (1.44 g,2.68 mmol) in MeOH (12 mL) was added a solution of pyridiniumpara-toluene sulphonate (0.67 g, 2.67 mmol) in MeOH (2.5 mL) in oneportion with stirring. Then pyridine-borage complex (325 mL, 2.67 mmol;M. in BH₃) was added dropwise and stirring was continued for 2.5 hoursat room temperature. The mixture was partitioned between EtOAc (400 mL)and 5% aqueous NaHCO₃ (100 mL). The organic layer was washed with 5%aqueous NaHCO₃ (2×75 mL), brine (75 mL) and dried (MgSO₄). The organiclayer was filtered and evaporated at reduced pressure. The resultantpale yellow foam (2.5 g) was applied to a silica gel column (4×38 cm),which was eluted first with MeOH—CH₂Cl₂ (1:50), then with MeOH—CH₂Cl₂(1:30). Evaporation of the appropriate fractions yielded 1.45 g (52%) ofthe title MMI-dimer as a colorless foam in high purity.

1H NMR ((CD₃)₂CO, 499.8 MHZ) (T1 and T2 represent 3′- and 5′-substitutedribo-thymidine moiety, respectively) d 1.08 (s, 18H, 2 CMe₃), 1.45 (d,3H, T1:C5-Me; J_(Me,H6)=0.7 Hz), 1.74 (d, 3H, T2:C5-Me, J_(MeH6)=1.0Hz), 2.52 (s, 3H, NMe), 2.54 (m, 1H, T1:H-3′), 2.80 (m, 1H, H-3Óa), 3.07(dd, 1H, H-3Ób; J_(3Óa,3Ób)=11.3, J_(3′,3Ób)=8.2 Hz), 3.21 (s, 3H, OMe),3.49 (t, 1H, T2:H-2′; J_(1′,2′)=4.1 Hz), 3.67 (dd, 1H, T2:H-5′a;J_(5′a,5′b)=11.2, J_(4′,5′a)=4.2 Hz), 3.84 (m, 1H, T2:H-5′b), 3.89 (dd,1H, T1:H-5′a; J_(5′a,5)′b=11.7, J_(4′,5′a)=4.2 Hz), 4.10-4.19 (3m, 3H,T1:H-5′b,H-4′, T2:H-4′), 4.23 (t, 1H, T2:H-3′; J_(3′,4′)=J_(2′,4′)=5.4Hz), 4.46 (m, 1H, T1:H-2′), 4.75 (d, 1H, 2′-OH; J_(2′,2″OH)=2.7 Hz),5.82 (d, 1H, T1:H-1′; J_(1′,2′)=2.2 Hz), 5.93 (d, 1H, T2:H-1′;J_(1′,2′)=3.7 Hz), 7.38-7.48, 7.66-7.69 and 7.71-7.77 (3m, 14H, 2H, 6H,4Ph, 2H-6) 9.98 (s, 2H, 2NH). ¹³C NMR ((CD₃)₂CO, 50.31 MHZ) d 12.01,12.40 (2C5-Me), 19.21, 19.42 (2CMe₃), 26.81, 27.03 (2CMe ₃), 38.89(NMe), 44.95 (T1:C-3′), 56.00 (T1:C-3Ó), 57.73 (OMe), 63.51 (T1:C-5′),70.36 (T2:C-5′,C-3′), 76.74 (T2:C-2′), 81.41 (T1:C-2′), 82.34, 83.38(2C-4′), 88.77, 92.28 (2C-1′), 110.50, 110.56 (2C-5), 127.65, 127.79,127.90, 127.94, 130.03, 130.08, 132.53, 132.77, 132.93, 133.01, 135.25,135.42, 135.59, 135.73 (4Ph,2C-6), 149.92, 150.71 (2C-4), 163.87, 164.09(2C-2). ES MS: m/z 1032.7 (M⁺); C₅₅H₆₉N₅O₁₁Si₂ requires 1032.5.

EXAMPLE 133′-De(oxyphosphinico)-3′-methylene(methylimino)-5′-O-DMT-5-methyluridinyl-(3>5)-3′-O-TBDPS-2′-O-methyl-5-methyluridine

A solution of3′-de(oxyphosphinico)-3′-methylene-(methylimino)-5′-O-TBDPS-5-methyluridinyl-(3>5)-3′-O-TBDPS-2′-O-methyl-5-methyluridine(0.765 g, 0.90 mmol), imidazole (0.100 g, 2.2 mmol) and TBDPSCl (0.317g, 1.15 mmol) in anhydrous CH₂Cl₂ (10 mL) was stirred at roomtemperature for six hours. A sample of the reaction mixture analyzed byTLC (10% MeOH in CH₂Cl₂) indicated that the reaction was only 50%completed. An additional amount of imidazole (0.100 g 2.2 mmol) alongwith TBDPSCl (0.317 g, 0.90 mmol) was added and the stirring wascontinued for additional 2 hours. The reaction mixture was diluted withCH₂Cl₂ (50 mL) and washed with a saturated aqueous NaHCO₃ solution (2×20mL), water (20 mL) and brine (20 mL). The organic layer was concentratedand purified by flash chromatography using a mixture ofethylacetate:hexane and methanol (60:35:5, v/v/v) as the eluant to give0.917 g (93%) of the title compound as a colorless foam.

¹H NMR (DMSO-d₆) δ 11.34 and 11.34 (2S, 2H), 7.25-7.17 (m, 21H)6.86-6.84 (m, 4H), 5.80 (d, 1H, J=2.2 Hz), 5.75 (d, 1H, J=2.4 Hz), 5.66(bs, 1H), 4.21 (m, 1H), 4.06 (m, 2H), 3.97-3.96 (m, 1H), 3.69 (s, 6H),3.52-3.51 (m, 1H), 3.49-3.37 (m, 3H), 3.32 (s, 3H), 3.12-3.07 (m, 4H),2.80 (bs, 1H), 2.32 (s, 2H), 1.64 (s, 3H), 1.33 (s, 3H) and 0.99 (s,9H). HRMS (FAB) for C₆₀H₆₉N₅O₁₃Si (MNa) 1118.4559, found 1118.4510.

EXAMPLE 143′-De(oxyphosphinico)-3′-methylene(methylimino)-5′-O-DMT-2′-O-acetyl-5-methyluridinyl-(3>5)-3′-O-TBDPS-2′-O-methyl-5-methyluridine

A solution of3′-de(oxyphosphinico)-3′-methylene(methylimino)-5′-O-DMT-5-methyluridinyl-(3>5)-3′-O-TBDPS-2′-O-methyl-5-methyluridine(0.800 g, 0.74 mmole), acetic anhydride (0.098 g, 0.96 mmole),triethylamine (0.133 g, 1.3 mmole) and DMAP (0.025 g, 0.20 mmole) inanhydrous CH₃CN (10 mL) was stirred at room temperature for 2 hours. TheTLC (10% MeOH in CH₂Cl₂) indicated the reaction was complete. Thesolvent was evaporated under reduced pressure and the residue wasdissolved in EtOAc (50 mL), washed with aqueous saturated bicarbonatesolution (2×10 mL) followed by water (10 mL). The organic layer wasdried over anhydrous Na₂SO₄, solvent was removed to give a residue whichwas purified by column chromatography using ethylacetate:hexane:MeOH(60:35:5, v/v/v) as the eluent to give 0.72 g (85%) of the titlecompound as a colorless foam.

¹H NMR (CDCl₃) δ 8.26 and 8.24 (2s, 2H), 7.70-7.15 (m, 21H), 6.84-6.79(m, 4H), 5.93 (d, 1H, J=3.6 Hz), 5.79 (=2.3 Hz), 5.65-5.55 (m, 1H),4.14-4.09 (m, 2H), 3.98-3.85 (m, 2H), 3.70 (bs, 7H), 3.60-3.50 (m, 3H),3.25 (s, 3H), 3.24-3.05 (m, 2H), 2.85-2.70 (m, 2H), 2.37 (bs, 2H), 2.08(s, 3H), 1.37 (s, 3H), 1.42 (s, 3H), 1.07 (s, 9H). HRMS (FAB) forC₆₂H₇₁N₅O₄Si (MNa) 1160.4664, found 1160.4702.

EXAMPLE 153′-De(oxyphosphinico)-3′-(methyleneimino)-5′-DMT-2′-O-acetyl-5-methyluridyl(3>5)-2′-O-methyl-5-methyluridine

A mixture of compound3′-de(oxyphosphinico)-3′-methylene(methylimino)-5′-O-DMT-2′-O-acetyl-5-methyluridinyl-(3>5)-3′-O-TBDPS-2′-O-methyl-5-methyluridine(0.70 g, 0.61 mmole) and TBAF on silica gel in anhydrous THF (10 mL) wasstirred at room temperature for 15 hours. A sample of the mixtureanalyzed by TLC using ethyl acetate:hexane:MeOH (70:20:10, v/v/v)indicated the reaction had gone to completion. The mixture was directlyloaded onto the silica gel column and eluted with the same solventsystem. The appropriate fractions were concentrated to a foam that wastriturated with ether. The resulting precipitate was removed byfiltration and dried to give 0.45 g (82%) of the title compound as acolorless foam.

¹H NMR, (DMSO-d6) δ 11.41 and 11.38 (2s, 2H), 7.59-7.26 (m, 15 H),6.91-6.86, (m, 4H), 5.83 (d, 1H, J=5.1 Hz), 5.79 (d, 1H, J=2.6 Hz),5.85-5.43 (m, 1H), 5.25-5.20 (m, 1H), 4.18-3.80 (m, 3H), 3.74 (s, 6H),3.34 (bs, 6H), 2.85-2.65, (m, 2H), 2.49 (bs, 2H), 2.09 (s, 3H), 1.73 (s,3H), 1.53 (s, 3H). HRMS (FAB) for C₄₆H₅₃N₅O₁₄ (MNa+) 922.3487, found922.3499.

EXAMPLE 163′-De(oxyphosphinico)-3′-(methyleneimino)-5′-DMT-2′-O-acetyl-5-methyluridylyl(3>5)-2′-O-methyl-5-methyluridine-3′-phosphoramidite

A mixture of3′-de(oxyphosphinico)-3′-(methyleneimino)-5′-DMT-2′-O-acetyl-5-methyluridylyl(3>5)-2′-O-methyl-5-methyluridine(0.417 g, 0.46 mmole), diisopropylaminotetrazolide (0.055 g, 0.31 mmole)and 2-cyanoethyl N,N,N′,N′teraisopropylphosphoramidite (0.208 g, 0.69mmole) in anhydrous CH₃CN (2.5 mL) was stirred at room temperature for 2hours. TLC using acetone:CH₂Cl₂ (1:1, v/v) showed only 50% reaction wascomplete. An additional 0.69 mmole of the reagent was added and thereaction stirred for total of 20 hours. The reaction mixture was dilutedwith EtOAc (50 mL), washed with brine (2×10 mL), and dried overanhydrous Na₂SO₄. The solvent was removed under reduced pressure to givea residual gum which was dissolved in CH₂Cl₂ (2 mL) and poured into avigorously stirred solution of hexane (125 mL). The stirring wascontinued for about 10 minutes and the solid was collected by filtrationand washed with hexane (2×10 mL). Drying gave 0.5 g and the colorlesssolid was dried under vacuum for 15 hours. Yield=0.500 g, 98% (90%purity by P-31 NMR, along with H-phosphonate of the reagent).

³¹P NMR (CD₃CN): δ 151.21 and 150.947 ppm HRMS (FAB) for C₅₅H₇₀N₇O₁₅P(MNa+) 1122.4565, found 1122.4522.

EXAMPLE 17 2′-O-Acetyl-3′-carboxymethyl-5′-O-DMT-5-methyluridine

5-Methyluridine is converted to the 5-O-DMT derivative and furtheracetylated using acetylbromide/DMAP. The2′-O-acetyl-5-O-DMT-5-methyluridine is converted to the 3′-allylderivative following a modification of Fiandor et al., TetrahedronLett., 1990, 31, 597. Oxidation of the 3′-allyl derivative to the acidis accomplished using sodium chlorite.

EXAMPLE 18 5′-Amino-3′-tBuPh₂Si-2′-O-methyl-5-methyluridine

5-Methyluridine was converted to5′-tosyl-3′-tBuPh₂Si-2′-O-methyl-5-methyluridine the title compoundusing methods described by DeMesmaeker, A., Agnew. Chem. Intl. Ed.Engl., 1994, 33, 226. The tosylate is displaced by lithium azide andreduced to give the amine.

EXAMPLE 193′-De(oxyphosphinico)-3′-(methylcarboxyamino)-5′-DMT-2′-O-acetyl-5-methyluridylyl(3>5)-2′-O-methyl-5-methyluridine-3′-phosphoramidite

The products of Examples 17 (acid) and 18 (amine) are condensed usingHBTU in DMF. The lower sugar moiety is deprotected at the 3′positionusing F⁻ in acid and phosphitylated to give the title modified dimer.The modified dimer is utilized further in the standard oligomersynthesis scheme illustrated in Example 30.

EXAMPLE 20 2′-O-(Chloroethoxyethyl)-3′-amino-5-methyl-5′-O-DMT-uridine

5-methyl-uridine is converted to 2′-O-(chloroethoxyethyl)-5-methyluridine according to the procedure of Yamakage described in TetrahedronLett, 1989, 30, 6361-6364. This material is converted to 3′-anhydroderivative by treating with diphenyl carbonate in DMF according to theprocedure described in “Nucleic Acids in Chemistry and Biology,” G. M.Blackburn and M. J. Gait, Oxford University Press 1996 p. 90. This3′-anhydro compound is treated with LiN₃/DMF to give2′-O-chloroethoxyethyl-3′-azido-5-methyl-uridine which on treatment withDMT-Cl/pyridine gave the corresponding 5-dimethoxytrityl derivative.This compound was reduced using dithiothreitol in 0.1 M phosphatebuffer/DMF according to the modification of a procedure suggested byHandlon and Oppenheimer described in Pharmaceutical Research, 1988, 5,297, to give the title compound.

EXAMPLE 21 2′-O-Methyl-3′-amino-5-methyl-5′-O-DMT-uridine

The procedure illustrated in Example 20 is repeated with2′-O-methyl-5-methyl-uridine (Chemgenes, Waltham, Mass.) as the startingmaterial. In this case, 2′-protection with a chloroethoxyethyl group isnot required to obtain the title compound.

EXAMPLE 22 Oligomer Synthesis

Solid support bound 2′-O-methyl-5-methyl-5′-O-DMT-uridine attached tosolid support through the 3′-O- is purchased from ChemGenes. The5′-O-DMT blocking group is removed as per standard protocols. The5′-hydroxyl group is phosphitylated to the 5′-H-phosphonate-2-cyanoethyldiester. The solid support bound material is coupled via oxidativephosphorylation to the product of Example 20 to give a modified dimer ina protected form. The modified dimer can be elongated by addition ofnucleosides and or nucleotides. Additional modified dimers are added bycoupling the product of Example 21 followed by the coupling of theproduct of Example 20. The chloroethoxyethyl group is removed during theoligonucleotide deprotection step by adjusting the pH to ca. 2.0.

EXAMPLE 23 2′-O-TBDPS-3′-carbony-5-methyl-5′-O-DMT-uridine

The title compound is prepared as adapted from the procedure of Xie etal., Tetrahedron Lett., 1996, 37, 4443-4446.

EXAMPLE 24 2′-O-Methyl-3′-carbony-5-methyl-5′-O-DMT-uridine

The title compound is prepared as adapted from the procedure of Samanoet al., Synthesis, 1991, 4, 282-288.

EXAMPLE 25 2′-O-TBDPS-3′-methylene-5-methyl-5′-O-DMT-uridine

The title compound is prepared from the product of Example 23 accordingto the procedure of Samano ibid.

EXAMPLE 26 2′-O-Methyl-3′-methylene-5-methyl-5′-O-DMT-uridine

The title compound is prepared from the product of Example 24 accordingto the procedure of Samano ibid.

EXAMPLE 27 2′-O-TBDPS-3′-(H-phosphonylmethyl)-5-methyl-5′-O-DMT-uridine

The title compound is prepared from the product of Example 25 accordingto the procedure of Nifantev et al., Chem. Abst., 1956, 50, 10124d.

EXAMPLE 28 2′-O-Methyl-3′-(H-phosphonylmethyl)-5-methyl-5′-O-DMT-uridine

The title compound is prepared from the product of Example 26 accordingto the procedure of Nifantev et al., Chem. Abst., 1956, 50, 10124d.

EXAMPLES 29-56 Procedures for the Preparation of Compounds of theFormula

wherein:

B is a heterocyclic base moiety and DMTr is dimethoxytrityl.

EXAMPLE 29Methyl-2-O-(2-ethylacetyl)-3,5-bis-O-(2,4-dichlorobenzyl)-α-D-ribofuranoside

1-O-Methyl-3,5-bis-O-(2,4-dichlorobenzyl)-α-D-ribofuranoside (preparedfrom 1-O-methyl-2,3,5-tris-O-(2,4-dichlorobenzyl)-α-D-ribofuranoside viathe literature procedure, Martin, P. Helv. Chem. Acta, 1995, 78,486-504) was dissolved in DMF (86 mL) with cooling to 5° C., and NaH(60% dispersion, 1.38 g, 34.38 mmol) was added. The reaction mixture wasstirred at 5° C. for 5 minutes then warmed to ambient temperature andstirred for 20 minutes after which time the reaction mixture was cooledto 5° C. and ethylbromoacetate (3.81 mL, 34.4 mmol) was added dropwiseresulting in the evolution of gas. The reaction mixture was allowed towarm to ambient temperature and stirred for 3 hours after which time themixture was cooled to 5° C. and the pH was adjusted to 3 with saturatedaqueous NH₄Cl. The solvent was evaporated in vacuo to give a syrup whichwas dissolved in EtOAc (200 mL), washed with water and then brine. Theorganic layer was separated, dried with MgSO₄, and the solvent wasevaporated in vacuo to give an oil. The oil was purified by flashchromatography using hexanes-EtOAc, 60:40, to give the title compound asan oil (15.52 g, 95%).

¹H NMR (CDCl₃): δ 7.58-7.18 (m, 6H), 5.05 (d, J=3.8 Hz, 1H), 4.79 (q,J_(AB)=13.7 Hz, 2H), 4.57 (d, J=2.8 Hz, 2H), 4.31-4.16 (m, 5H), 4.03 (m,2H), 3.62 (d, 2H), 3.50 (s, 3H), 1.28 (t, 3H). ¹³C NMR (CDCl₃): δ 170.0,134.2, 133.6, 133.5, 130.3, 129.8, 129.1, 128.8, 127.1, 102.1, 81.4,78.9, 76.6, 70.6, 70.0, 69.3, 67.6, 61.0, 55.6, 14.2. Anal. Calcd forC₂₄H₂₆Cl₄O₇.H₂O: C, 49.17; H, 4.81. Found: C, 49.33; H, 4.31.

EXAMPLE 301-[2′-O-(2-Ethylacetyl)-3′,5′-bis-O-(2,4-dichlorobenzyl)-β-ribofuranosyl]thymine

Thymine (6.90 g, 54.6 mmol) was suspended in anhydrous dichloroethane(136 mL) and bis-trimethylsilylacetamide (40.5 mL, 164 mmol) was added.The reaction mixture was heated to reflux temperature for 10 minutes togive dissolution. After cooling to ambient temperature, the solution wasadded to compoundmethyl-2-O-(2-ethylacetyl)-3,5-bis-o-(2,4-dichlorobenzyl)-α-D-ribofuranosidewith stirring. Trimethylsilyl trifluoromethanesulfonate (6.86 mL, 35.5mmol) was added and the reaction mixture was heated to reflux for 6hours. The mixture was cooled to 5° C. and the pH was adjusted to 7 bythe slow addition of saturated NaHCO₃. The mixture was extracted withCH₂Cl₂ (3×150 mL) and the organic extracts were combined, washed withbrine, and the solvent was evaporated in vacuo to give an oil. The oilwas dissolved in CH₂Cl₂ and purified by flash chromatography usinghexanes-EtOAc, 45:55, to provide the title compound as an oil (7.92 g,44%). (The α-anomer was contained in a later fraction).

¹H NMR (400 MHZ, CDCl₃): δ 8.25 (s, 1H), 7.67 (s, 1H), 7.46-7.21 (m,6H), 5.94 (d, J=1.6 Hz, 1H), 4.80 (q, J_(AB)=12.4 Hz, 2H), 4.70-4.18 (m,9H), 4.02 (d, 1H), 3.75 (d, 1H), 1.58 (s, 3H), 1.26 (t, 3H). ¹³C NMR(CDCl₃): δ 170.1, 164.3, 150.3, 135.5, 134.5, 134.2, 134.1, 133.8,133.5, 130.7, 130.2, 129.4, 129.0, 127.1, 110.3, 88.4, 80.8, 80.5, 74.7,70.1, 68.9, 68.0, 66.2, 60.9, 14.1, 12.1. Anal. Calcd forC₂₈H₂₈Cl₄N₂O₈.H₂O: C, 49.43; H, 4.44; N, 4.12. Found: C, 49.25; H, 4.10;N, 3.94.

EXAMPLE 311-[2′-O-(2-Hydroxyethyl)-3′,5′-bis-O-(2,4-dichlorobenzyl)-β-D-ribofuranosyl]thymine

1-[2′-O-(2-Ethylacetyl)-3′,5′-bis-O-(2,4-dichlorobenzyl)-β-D-ribofuranosyl]thymine(9.92 g, 15.0 mmol) was dissolved in hot EtOH (150 mL) and the solutionwas cooled to ambient temperature in a water bath. To the solution wascautiously added NaBH₄ (1.13 g, 30.0 mmol) over 10 minutes. After 3hours additional NaBH₄ (282 mg, 7.45 mmol) was added the mixture wasstirred for 1 hour and left to stand for 8 hours. The pH was adjusted to4 by addition of Saturated NH₄Cl (25 mL) to give a gum. The solvent wasdecanted and evaporated in vacuo to afford a white solid which wasdissolved in CH₂Cl₂ (250 mL). The gum was dissolved with saturatedaqueous NaHCO₃ and this solution was gently extracted with the CH₂Cl₂containing the product. The organic layer was separated and the aqueouslayer was extracted again with CH₂Cl₂ (2×50 mL). After combining theorganic layers, the solvent was dried over MgSO₄ and evaporated in vacuoto afford a white foam. The foam was dissolved in CH₂Cl₂ and purified byflash chromatography using hexanes-EtOAc, 20:80, to give the titlecompound as a white foam (8.39 g, 90%).

¹H NMR (CDCl₃): δ 10.18 (s, 1H), 7.66 (s, 1H), 7.39-7.20 (m, 6H), 5.96(s, 1H), 4.76-3.62 (m, 14H), 1.58 (s, 3H). ¹³C NMR (CDCl₃): δ 164.0,150.8, 135.2, 134.6, 134.2, 134.1, 133.5, 133.4, 130.2, 129.4, 129.0,127.1, 110.6, 88.6, 81.0, 80.7, 75.2, 72.0, 70.1, 68.9, 68.1, 61.9,12.1.

EXAMPLE 321-[2′-O-(2-Phthalimido-N-hydroxyethyl)-3′,5′-bis-O-(2,4-dichlorobenzyl)-β-D-ribofuranosyl]thymine

1-[2′-O-(2-Hydroxyethyl)-3′,5′-bis-O-(2,4-dichlorobenzyl)-β-D-ribofuranosyl]thyminewas dried by coevaporation with anhydrous acetonitrile followed byfurther drying in vacuo (0.1 torr) at ambient temperature for 12 h. Thedried material (8.39 9, 13.53 mmol) was dissolved in freshly distilledTHF (97 mL), PPh₃ (3.90 g, 14.9 mmol), and N-hydroxyphthalimide (2.43 g,14.9 mmol) was added. The reaction mixture was cooled to −78° C., anddiethyl azodicarboxylate (2.34 mL, 14.9 mmol) was added. The reactionmixture was warmed to ambient temperature and the solvent was evaporatedin vacuo to give a foam. The foam was dissolved in EtOAc (100 mL) andwashed with saturated aqueous NaHCO₃ (3×30 mL). The organic layer wasseparated, washed with brine, dried over MgSO₄, and the solventevaporated to give a foam. The foam was purified by flash chromatographyusing CH₂Cl₂-acetone, 85:15, to give the title compound as a white foam(3.22 g, 31%). A second chromatographic purification provided additionaltitle compound as a white foam (5.18 g, 50%).

¹H NMR (400 MHZ, CDCl₃): δ 9.0 (s, 1H), 7.8 (m, 11H) 5.95 (s, 1H),4.84-3.70 (m, 13H), 1.60 (s, 3H). ¹³C NMR (100 MHZ, CDCl₃): δ 163.7,163.5, 150.2, 138.0, 135.6, 134.5, 134.1, 134.0, 133.9, 133.7, 133.6,130.6. 130.4, 130.1, 129.8, 129.4, 129.1, 129.0, 128.8, 127.2, 123.5,110.4, 88.2, 81.0, 80.9, 77.6, 75.4, 70.2, 68.9, 68.4, 68.1., 12.1. LRMS(FAB+) m/z: 766 (M+H). LRMS (FAB−) m/z: 764 (M−H).

EXAMPLE 331-[2′-O-(2-Phthalimido-N-oxyethyl)-3′,5′-bis-O-(2,4-dichlorobenzyl)-β-D-ribofuranosyl]thymine

1-[2′-O-(2-phthalimido-N-hydroxyethyl)-3′,5′-bis-O-(2,4-dichlorobenzyl)-β-D-ribofuranosyl]thymine(1.79 g, 2.34 mmol) was dissolved in CH₂Cl₂ (12 mL), the solution wascooled to −78° C. and 1.0 M boron trichloride (5.15 mL, 5.15 mmol) inCH₂Cl₂ was added and the reaction mixture was kept at 5° C. for 1.5hours. Additional 1.0 M boron trichloride (5.15 mL, 5.15 mmol) in CH₂Cl₂was added and the solution was stirred at 5° for an additional 1.5hours. The pH was adjusted to 7 with saturated aqueous NaHCO₃ (30 mL).After dilution with CH₂Cl₂ (100 mL), the organic layer was separated,and the aqueous layer was extracted with CHCl₃ (5×25 mL) and then EtOAc(3×25 mL). The organic layers were combined, dried over Na₂SO₄, andevaporated in vacuo to give an oil. The oil was purified by flashchromatography using CH₂Cl₂-acetone, 45:55, to provide the titlecompound as a white foam (619 mg, 59%).

¹H NMR (CDCl₃): δ 8.8 (br, 1H), 7.88-7.75 (m, 4H), 7.50 (s, 1H), 5.70(d, J=4 Hz, 1H), 4.45-3.75 (m, 11H), 2.95 (br, 1H), 1.90 (s, 3H). ¹³CNMR (100 MHZ, CDCl₃): δ 164.3, 163.7, 150.6, 137.4, 134.7, 128.5, 123.6,110.5, 89.7, 84.7, 81.9, 77.6, 68.5, 68.4, 61.0, 12.3. LRMS (FAB+) m/z:448 (M+H). LRMS (FAB−) m/z: 446 (M−H).

EXAMPLE 341-[2′-O-(2-Phthalimido-N-oxyethyl)-5′-O-(4,4′-dimethoxytrityl)-β-D-ribofuranosyl]thymine

1-[2′-O-(2-phthalimido-N-oxyethyl)-3′,5′-bis-O-(2,4-dichlorobenzyl)-β-D-ribofuranosyl]thyminewas dried by coevaporation with anhydrous acetonitrile followed byfurther drying in vacuo (0.1 torr) at ambient temperature for 12 hours.The dried material (619 mg, 1.38 mmol) was dissolved in anhydrouspyridine (7 mL) and 4,4′-dimethoxytrityl chloride (514 mg, 1.52 mmol)was added. After 2 hours additional 4,4′-dimethoxytrityl chloride (257mg, 0.76 mmol) was added. The solution was stirred for 2 hours and afinal addition of 4,4′-dimethoxytrityl chloride (257 mg, 0.76 mmol) wasmade. After 12 h MeOH (10 mL) was added to the reaction mixture, it wasstirred for 10 min and the solvent was evaporated in vacuo to give anoil which was coevaporated with toluene. The oil was purified by flashchromatography by pre-treating the silica with CH₂Cl₂-acetone-pyridine,80:20:1, then using CH₂Cl₂-acetone, 80:20 to afford the title compoundas a yellow solid (704 mg, 68%).

¹H NMR (CDCl₃): δ 7.8-6.8 (m, 18H), 5.94 (d, J=2.2 Hz, 1H), 4.57-4.12(m, 7H), 3.78 (s, 6H), 3.53 (m, 2H), 1.34 (s, 3H). ¹³C NMR (CDCl₃): δ164.3, 163.8, 158.6, 150.6, 144.4, 135.5, 135.4, 134.7, 130.1, 128.7,128.2, 128.0, 127.1, 123.7, 113.3, 110.9, 87.9, 86.7, 83.2, 68.7, 68.5,61.7, 55.2, 11.9. LRMS (FAB+) m/z: 750 (M+H). LRMS (FAB−) m/z: 748(M−H). Anal. Calcd for C₄₁H₃₉N₃O₁₁.H₂O: C, 65.14; H, 5.38; N, 5.47.Found: C, 63.85; H, 5.16; N, 5.14. Anal. Calcd for C₄₁H₃₉N₃O₁₁: C,65.68; H, 5.24; N, 5.60. Found: C, 65.23; H, 5.27; N, 5.45.

EXAMPLE 351-[2′-O-(2-Phthalimido-N-oxyethyl)-5′-O-(4,4′-dimethoxytrityl)-β-D-ribofuranosyl]thymine-3′-[(2-cyanoethyl)-N,N-diisopropylphosphoramidite]

1-[2′-O-(2-phthalimido-N-oxyethyl)-5′-O-(4,4′-dimethoxytrityl)-β-D-ribofuranosyl]thyminewas dried by coevaporation with anhydrous pyridine (2×20 mL), thenfurther dried in vacuo (0.1 torr) at ambient temperature for 12 hours.The dried material (704 mg, 0.939 mmol) was dissolved in CH₂Cl₂ (9 mL),diisopropylamine tetrazolide (80.4 mg, 0.47 mmol) and2-cyanoethyl-N,N,N′,N′-tetraisopropylphosphorodiamidite (0.33 mL, 1.03mmol) with stirring. After 2 hours at ambient temperature additional2-cyanoethyl-N,N,N′,N′-tetra-isopropylphosphorodiamidite (0.33 mL, 1.03mmol) was added and the solution was stirred for 20 hours. The solventwas evaporated in vacuo to give an oil which was purified by flashchromatography by pre-treating the silica with CH₂Cl₂-acetone-pyridine,85:15:1, then using CH₂Cl₂-acetone, 85:15 to afford the title compoundas an oil (704 mg, 68%). The product was coevaporated with anhydrousacetonitrile (2×30 mL) and CH₂Cl₂ (2×30 mL) to afford a yellow foam.

¹H NMR (CDCl₃): δ 8.6 (br, 1H), 7.78-6.82 (m, 18H), 6.06 (m, 1H),4.6-3.3 (m, 14H), 3.75 (s, 6H), 2.66 (m, 1H), 2.37 (m, 1H), 1.36 (s,3H), 1.16 (m, 12H). ³¹P NMR (CDCl₃): δ 150.5, 151.2. LRMS (FAB+) m/z:950 (M+H). LRMS (FAB−) m/z: 948 (M−H). Anal. Calcd for C₅₀H₅₆N₅O₁₂P.H₂O:C, 62.04; H, 6.04; N, 7.24. Found: C, 62.20; H, 5.94; N, 7.34.

EXAMPLE 362′-O-(2-Ethylacetyl)-3′,5′-O-(1,1,3,3-tetraisopropyldisiloxane-1,3-diyl)adenosine

Adenosine (30.00 g, 112 mmol) was dissolved in hot anhydrous DMF (600mL) and the solution was cooled to ambient temperature. NaH (60%dispersion oil, 4.94 g, 124 mmol) was added and the mixture was stirredwith a mechanical stirrer for 1 hour. The resulting suspension wascooled to 5° C. and ethylbromoacetate (13.7 mL, 124 mmol) was added. Theresulting solution was stirred for 12 hours at ambient temperature andthe solvent was evaporated in vacuo to give a residue which contained2′-O-(2-ethylacetyl)adenosine and the putative 3′-O-isomer. Thismaterial was coevaporated with pyridine to give a foam which wasdissolved in anhydrous pyridine (400 mL).1,3-Dichloro-1,1,3,3-tetraisopropyldisiloxane (39.52 mL, 124 mmol) wasadded and the solution was stirred for 24 hours at ambient temperature.The solvent was evaporated in vacuo to give an oil which was dissolvedin EtOAc (500 mL) and washed with brine three times. The organic layerwas separated, dried over MgSO₄, and the solvent was evaporated in vacuoto afford an oil. The oil was purified by flash chromatography usinghexanes-EtOAc, 80:20, to give the title compound as an oil (14.63 g,22%).

¹H NMR (CDCl₃): δ 8.26 (s, 1H), 8.07 (s, 1H), 6.20 (br s, 2H), 4.91 (dd,J_(1′,2′)=4.7 Hz, J_(2′,3′)=9.3 Hz, 1H), 4.64-3.97 (m, 8H), 1.22 (t,3H), 1.05 (m, 28 H). ¹³C NMR (CDCl₃): δ 170.0, 155.5, 152.8, 149.0139.3, 120.2, 88.6, 82.2, 81.1, 69.9, 68.3, 60.8, 60.0, 17.2, 14.0,12.7. Anal. Calcd for C₂₆H₄₅N₅O₇Si₂: C, 52.41; H, 7.61; N, 11.75, Si,9.43. Found: C, 52.23; H, 7.34; N, 11.69.

EXAMPLE 372′-O-(2-Hydroxyethyl)-3′,5′-O-(1,1,3,3-tetraisopropyldisiloxane-1,3-diyl)adenosine

2′-O-(2-ethylacetyl)-3′,5′-O-(1,1,3,3-tetraisopropyldisiloxane-1,3-diyl)adenosine(4.175 g, 7.01 mmol) was dissolved in ethanol (95%, 40 mL) and theresulting solution was cooled to 5° C. NaBH₄ (60% oil dispersion, 0.64g, 16.8 mmol) was added, and the mixture was allowed to warm to ambienttemperature. After stirring for 12 hours CH₂Cl₂ (200 mL) was added andthe solution was washed with brine twice and the organic layer wasseparated. The organic layer was dried over MgSO₄, and the solvent wasevaporated in vacuo to give an oil. The oil was purified by flashchromatography using EtOAc-MeOH, 95:5, to afford the title compound asan oil (0.368 g, 9.5%).

¹H NMR (CDCl₃): δ 8.31 (s, 1H), 8.14 (s, 1H), 6.18 (br s, 2H), 6.07 (s,1H), 4.62 (dd, J_(1′,2′)=4.6 Hz, J_(2′,3′)=9.4 Hz, 1H), 4.3-3.5 (m, 8H),1.03 (m, 28H). ¹³C NMR (CDCl₃): δ 155.5, 153.0, 148.7, 138.3, 120.3,89.2, 82.7, 81.4, 73.5, 69.3, 61.8, 59.7, 17.2, 17.0, 16.8, 13.4, 12.9,12.8, 12.6. LRMS (FAB+) m/z: 554 (M+H), 686 (M+Cs+).

EXAMPLE 382′-O-(2-Phthalimido-N-hydroxyethyl)-3′,5′-O-(1,1,3,3-tetraisopropyldisiloxane-1,3-diyl)adenosine

To a solution of2′-O-(2-hydroxyethyl)-3′,5′-O-(1,1,3,3-tetraisopropyldisiloxane-1,3-diyl)adenosine(0.330 g, 0.596 mmol) in anhydrous THF (10 mL) was addedtriphenylphosphine (0.180 g, 0.685 mmol) and N-hydroxyphthalimide (0.112g, 0.685 mmol). To this mixture diethyl azodicarboxylate (0.11 mL, 685mmol) was added dropwise at 5° C. After stirring for 3 hours at ambienttemperature, the solvent was evaporated to give an oil. The oil wasdissolved in EtOAc and washed with saturated aqueous NaHCO₃ (×3) andbrine. The organic layer was separated, dried over MgSO₄. The solventwas evaporated in vacuo to give an oil. The oil was purified by flashchromatography using EtOAc-MeOH, 95:5, to give the title compound as anoil (0.285 g, 68%).

¹H NMR (CDCl₃): δ 8.21 (s, 1H), 8.05 (s, 1H), 7.8-7.45 (m, 4H), 6.00 (s,1H), 5.88 (br s, 2H), 4.92 (dd, J_(1′,2′)=4.6, J_(2′,3′)=9.0 Hz),4.5-3.9 (m, 8H), 1.0 (m, 28H). ¹³C NMR (CDCl₃): δ 163, 155.3, 152.8,149, 139.6, 134.3, 123.4, 120, 88.7, 82.7, 81.1, 77.4, 70.2, 69.5, 60.1,17.4, 17.2, 17.0, 16.9, 13.3, 12.9, 12.7, 12.6. LRMS (FAB+) m/z: 699(M+H).

EXAMPLE 39N6-Benzoyl-2′-O-(2-Phthalimido-N-hydroxyethyl)-3′,5′-O-(1,1,3,3-tetraisopropyldisiloxane-1,3-diyl)adenosine

To a solution of2′-O-(2-Phthalimido-N-hydroxyethyl)-3′,5′-O-(1,1,3,3-tetraisopropyldisiloxane-1,3-diyl)adenosine(1.09 g, 1.97 mmol) in anhydrous pyridine (19 mL) cooled to 5° C. wasadded benzoyl chloride (1.14 mL, 9.8 mmol) and the resulting mixture wasstirred at ambient temperature for 12 hours. After cooling the mixtureto 5° C., cold water (3.8 mL) was added, the mixture was stirred for 15minutes, and conc NH₄OH (3.8 mL) was added. After stirring for 30minutes at 5° C. the solvent was evaporated to give a residue which wasdissolved in water and extracted with CH₂Cl₂ three times. The organicextracts were combined, dried over MgSO₄, and evaporated in vacuo toafford an oil. The oil was purified by flash chromatography usinghexanes-EtOAc, 50:50, then 20:80, to give the title compound as an oil(0.618 g, 48%).

¹H NMR (CDCl₃): δ 9.2 (br s, 1H), 8.69 (s, 1H), 8.27 (s, 1H), 8.0-7.4(m, 9H), 6.12 (s, 1H), 4.95 (dd, J_(1′,2′)=4.7 Hz, J_(2′,3′)=9.1 Hz,1H), 4.5-4.0 (m, 8H), 1.06 (m, 28H). ¹³C NMR (CDCl₃): δ 164.4, 163.3,152.5, 150.8, 149.3, 142.1, 134.4, 133.7, 132.6, 132.1, 128.7, 128.2,127.7, 123.4, 88.9, 82.7, 81.3, 77.5, 70.1, 69.6, 60.0, 17.2, 17.0,16.8, 13.3, 12.8, 12.7, 12.6. LRMS (FAB+) m/z: 803 (M+H).

EXAMPLE 40 N⁶-Benzoyl-2′-O-(2-Phthalimido-N-hydroxyethyl)adenosine

To a solution ofN6-Benzoyl-2′-O-(2-phthalimido-N-hydroxyethyl)-3′,5′-O-(1,1,3,3-tetraisopropyldisiloxane-1,3-diyl)adenosine(0.680 g, 0.847 mmol) in THF (20 mL) in a polyethylene reaction vesselat 5° C. was added HF-pyridine (70%, 0.48 mL, 16.9 mmol) and theresulting mixture was warmed to ambient temperature. After stirring for12 hours the solvent was evaporated in vacuo, EtOAc was added, thesolution was washed with water, and the aqueous layer was separated andextracted with EtOAc. The organic layers were combined, dried overMgSO₄, and the solvent was evaporated in vacuo to give the titlecompound as a solid (408 mg, 86%).

¹H NMR (DMSO-d₆): δ 11.2 (br s, 1H), 8.71 (s, 1H), 8.67 (s, 1H), 8.0-7.5(m, 9H), 6.11 (d, J1′,2′=5.7 Hz), 5.23 (d, 1H), 5.14 (t, 1H), 4.66 (t,1H), 4.35 (m, 3H), 3.90 (m, 3H), 3.6 (m, 2H). ¹³C NMR (DMSO-d₆): δ163.5, 152.0, 143.2, 135.0, 132.6, 131.9, 131.7, 129.3, 128.7, 128.5,123.4, 86.3, 85.8, 81.3, 76.8, 69.0, 68.7, 61.3. LRMS (FAB+) m/z: 561(M+H, 583 (M+Na+).

EXAMPLE 41N⁶-Benzoyl-2′-O-(2-Phthalimido-N-oxyethyl)-5′-O-(4,4′-dimethoxytrityl)adenosine

To a solution of N⁶-Benzoyl-2′-O-(2-phthalimido-N-hydroxyethyl)adenosine(0.258 g, 0.46 mmol) in anhydrous pyridine (5 mL) was added4,4′-dimethoxytrityl chloride (0.179 g, 0.53 mmol) and the solution wasstirred for 12 hours at ambient temperature. Water was added and themixture was extracted with EtOAc three times. The organic extracts werecombined, evaporated in vacuo, and dried over MgSO₄. The resulting oilwas purified by flash chromatography using hexanes-EtOAc, 90:10, to givethe title compound as an oil (0.249 g, 63%).

¹H NMR (CDCl₃): δ 9.16 (br s, 1H), 8.68 (s, 1H), 8.28 (s, 1H), 8.1-6.8(m, 22H), 6.26 (d, J 1′,2′=4.0 Hz, 1H), 4.76 (m, 1H), 4.60 (m, 1H),4.4-4.3 (m, 3H), 4.13-4.0 (m, 3H), 3.77 (s, 6H), 3.48 (m, 2H). ¹³C NMR(CDCl₃): δ 164.5, 163.6, 158.5, 152.6, 151.4, 149.5, 144.5, 141.9,135.7, 134.7, 132.7. 130.1, 128.8, 128.2, 127.8, 126.9, 123.7, 113.2,87.2, 84.1, 82.6, 69.9, 69.0, 63.0, 60.3, 55.2. HRMS (FAB+) m/z (M+Cs+)calcd for C₄₈H₄₂N₆O₁₀ 995.2017, found 995.2053 (M+Cs+).

EXAMPLE 42N⁶-Benzoyl-2′-O-(2-Phthalimido-N-oxyethyl)-5′-O-(4,4′-dimethoxytrityl)adenosine-3′-[(2-cyanoethyl)-N,N-diisopropylphosphoramidite]

To a solution ofN⁶-benzoyl-2′-O-(2-phthalimido-N-oxyethyl)-5′-O-(4,4′-dimethoxytrityl)adenosine(0.300 g, 0.348 mmol) in CH₂Cl₂ (10 mL) was added diisopropylaminetetrazolide (0.030 g, 0.174 mmol) and2-cyanoethyl-N,N,N′,N′-tetraisopropylphosphorodiamidite (0.13 mL, 0.418mmol). After stirring for 12 hours at ambient temperature additionaldiisopropylamine tetrazolide (0.060 g, 0.348 mmol) and2-cyanoethyl-N,N,N′,N′-tetraisopropylphosphorodiamidite (0.26 mL, 0.832mmol) were added in two portions over 24 hours. After 24 hoursCH₂Cl₂-NEt₃, 100:1, was added and the mixture was washed with saturatedaqueous NaHCO₃ and brine. The organic layer was separated, dried overMgSO₄, and the solvent was evaporated in vacuo. The resulting oil waspurified by flash chromatography by pre-treating the silica withhexanes-EtOAc-NEt₃, (40:60:1), then using the same solvent system togive the title compound as an oil (203 g, 55%).

¹H NMR (CDCl₃): δ 6.27 (m, 1H). ³¹P NMR (CDCl₃): δ 151.0, 150.5. HRMS(FAB+) m/z (M+Cs+) calcd for C₅₇H₅₉N₈O₁₁P 1195.3095, found 1195.3046(M+Cs+).

EXAMPLE 432′-O-(2-Aminooxyethyl)-3′,5′-O-(1,1,3,3-tetraisopropyldisiloxane-1,3-diyl)adenosine

To a solution of2′-O-(2-Phthalimido-N-hydroxyethyl)-3′,5′-O-(1,1,3,3-tetraisopropyldisiloxane-1,3-diyl)adenosine(0.228 g, 0.326 mmol) in CH₂Cl₂ (5 mL) at 5° C. was addedmethylhydrazine (0.017 mL, 0.326 mmol) with stirring for 2 hours. Themixture was filtered to remove a precipitate and the filtrate was washedwith water and brine. The organic layer was separated, dried over MgSO₄,and the evaporated in vacuo to give the title compound as an oil (186mg). The oil was of sufficient purity for subsequent reactions.

¹H NMR (CDCl₃): δ 8.31 (s, 1H), 8.15 (s, 1H), 6.07 (s, 1H), 5.78 (br s,2H), 4.70 (dd, J 1′,2′=4.4 Hz, J 2′,3′=9.0 Hz, 1H), 4.3-3.9 (m, 8H), 1.9(br, 2H), 1.0 (m, 28H). LRMS (FAB+) m/z: 569 (M+H), 702 (M+Cs+).

EXAMPLE 442′-O-(2-O-Formaldoximylethyl)-3′,5′-O-(1,1,3,3-tetraisopropyldisiloxane-1,3-diyl)adenosine

To a solution of2′-O-(2-aminooxyethyl)-3′,5′-O-(1,1,3,3-tetraisopropyldisiloxane-1,3-diyl)adenosine(0.186 g, 0.326 mmol) in EtOAc (2 mL) and MeOH (2 mL) was addedformaldehyde (aqueous 37%, 0.028 mL, 0.342 mmol) with stirring atambient temperature for 3 hours. The solvent was evaporated in vacuo togive the title compound as an oil (189 mg). The oil was of sufficientpurity for subsequent reactions.

¹H NMR (CDCl₃): δ 8.31 (s, 1H), 8.09 (s, 1H), 6.97 (d, J=8.3 Hz, 1H),6.38 (d, J=8.3 Hz, 1H), 6.01 (s, 1H), 5.66 (br s, 2H), 4.77 (dd,J_(1′,2′)=4.7 Hz, J_(2′,3′)=9.3 Hz), 4.3-4.0 (m, 8H), 1.0 (m, 28H). LRMS(FAB+) m/z: 581 (M+H), 713 (M+Cs⁺).

EXAMPLE 45N⁶-Benzoyl-2′-O-(2-O-formaldoximylethyl)-3′,5′-O-(1,1,3,3-tetraisopropyldisiloxane-1,3-diyl)adenosine

To a solution of2′-O-(2-O-Formaldoximylethyl)-3′,5′-(1,1,3,3-tetraisopropyldisiloxane-1,3-diyl)adenosine(0.189 g, 0.326 mmol)in pyridine (5 mL) at 5° C. was added benzoylchloride (0.19 mL, 1.63 mmol) and the resulting solution was stirred atambient temperature for 3 hours. The solution was cooled to 5° C. andconcentrated NH₄OH (1.5 mL) was added with stirring for 1 hour. Thesolvent was evaporated. in vacuo to give an oil which was dissolved inCH₂Cl₂. The solution was washed with water and the organic layer wasseparated, dried with MgSO₄, and the solvent was evaporated to give thetitle compound (223 mg) as an oil which was of sufficient purity forsubsequent reactions.

¹H NMR (CDCl₃): δ 9.30 (br, 1H), 8.79 (s, 1H), 8.31 (s, 1H), 8.1-7.2 (m,5H), 7.00 (d, 1H), 6.39 (d, 1H), 6.09 (s, 1H), 4.77 (dd, 1H), 4.4-3.9(m, 8H), 1.1 (m, 28H).

EXAMPLE 46 N⁶-Benzoyl-2′-O-(2-O-formaldoximylethyl)adenosine

To a solution ofN⁶-benzoyl-2′-O-(2-O-formaldoximylethyl)-3′,5′-O-(1,1,3,3-tetraisopropyldisiloxane-1,3-diyl)adenosine(223 mg, 0.326 mmol)in THF (10 mL) in a polyethylene reaction vessel at5° C. was added HF-pyridine (70%, 0.19 mL, 6.5 mmol) and the mixture wasallowed to warm to ambient temperature. After stirring for 48 hours thesolvents were evaporated in vacuo to give a residue which was dissolvedin EtOAc and washed with water. The organic layer was separated, theaqueous layer was extracted with EtOAc, and the organic layers werecombined, dried over MgSO₄, and evaporated in vacuo. The resultingresidue was purified by flash chromatography using EtOAc-MeOH, 95:5, togive the title compound as a solid (24 mg, 17%).

¹H NMR (CDCl₃): δ 9.05 (br s, 1H), 8.77 (s, 1H), 8.13 (s, 1H), 7.9-7.2(m), 6.26 (d, J=10.7 Hz, 1H), 6.03 (d, J_(1′,2′)7.8 Hz), 4.88 (dd, J=4.6Hz, J=7.9 Hz, 1H), 4.6-3.7 (m, 10H). LRMS (FAB+) m/z: 443 (M+H). LRMS(FAB−) m/z: 441 (M−H).

EXAMPLE 47N6-Benzoyl-2′-O-(2-O-formaldoximylethyl)-5′-O-(4,4′-dimethoxytrityl)adenosine

To a solution of N⁶-benzoyl-2′-O-(2-O-formaldoximylethyl)adenosine (0.34g, 0.768 mmol)in pyridine (7 mL) was added 4,4′-dimethoxytrityl chloride(0.312 g, 0.922 mmol) and the reaction mixture was stirred at ambienttemperature for 5 hours. Additional amounts of 4,4′-dimethoxytritylchloride (520 mg, 1.54 mmol and 340 mg, 0.768 mmol) were added over 24hours. The solvent was evaporated, the crude product was dissolved inEtOAc, and washed with water. The organic layer was separated, driedover MgSO₄ and the solvent was evaporated in vacuo. The crude materialwas purified by column chromatography using EtOAc-Hexanes-NEt₃,80:20:0.5, v/v/v, followed by, EtOAc-NEt3, 100:0.5, v/v, as solvent togive the title compound as an oil (0.269 g, 47%).

¹H NMR (CDCl₃): δ 8.99 (br s, 1H), 8.74 (s, 1H), 8.1-6.8 (m, 18H), 7.00(d, 1H), 6.43 (d, 1H), 6.19 (d, 1H), 4.72 (m, 1H), 4.48 (m, 1H), 4.23(m, 3H), 4.1 (m, 1H), 3.9 (m, 1H), 3.78 (s, 6H), 3.45 (m, 2H), 3.15 (d,1H). HRMS (FAB+) m/z (M+Cs+) calcd for C₄₁H₄₀N₆O₈ 877.1962, found877.1988 (M+Cs+).

EXAMPLE 48 2′-O-Allyl-5′-O-dimethoxytrityl-5-methyluridine

In a 100 mL stainless steel pressure reactor, allyl alcohol (20 mL) wasslowly added to a solution of borane in tetrahydrofuran (1 M, 10 mL, 10mmol) with stirring. Hydrogen gas rapidly evolved. Once the rate ofbubbling subsided, 2,2′-anhydro-5-methyluridine (1.0 g, 0.4.2 mmol) andsodium bicarbonate (6 mg) were added and the reactor was sealed. Thereactor was placed in an oil bath and heated to 170° C. internaltemperature for 18 hours. The reactor was cooled to room temperature andopened. Tlc revealed that all the starting material was gone (startingmaterial and product Rf 0.25 and 0.60 respectively in 4:1 ethylacetate/methanol on silica gel). The crude solution was concentrated,coevaporated with methanol (50 mL), boiling water (15 mL), absoluteethanol (2×25 mL) and then the residue was dried to 1.4 g of tan foam (1mm Hg, 25° C., 2 hours). A portion of the crude nucleoside (1.2 g) wasused for the next reaction step without further purification. Theresidue was coevaporated with pyridine (30 mL) and redissolved inpyridine (30 mL). Dimethoxytrityl chloride (1.7 g, 5.0 mmol) was addedin one portion at room temperature. After 2 hours the reaction wasquenched with methanol (5 mL), concentrated in vacuo and partitionedbetween a solution of saturated sodium bicarbonate and ethyl acetate(150 mL each). The organic phase was separated, concentrated and theresidue was subjected to column chromatography (45 g silica gel) using asolvent gradient of hexanes-ethyl acetate-triethylamine (50:49:1) to(60:39:1). The product containing fractions were combined, concentrated,coevaporated with acetonitrile (30 mL) and dried (1 mm hg , 25° C., 24hours) to 840 mg (34% two-step yield) of white foam solid. The NMR wasconsistent with the unmethylated uridine analog reported in theliterature.

EXAMPLE 49 2′-O-(2-Hydroxyethyl)-5′-O-dimethoxytrityl-5-methyluridine

2′-O-Allyl-5′-O-dimethoxytrityl-5-methyluridine (1.0 g, 1.6 mmol),aqueous osmium tetroxide (0.15 M, 0.36 mL, 0.0056 mmol, 0.035 eq) and4-methylmorpholine N-oxide (0.41 g, 3.5 mmol, 2.15 eq) were dissolved indioxane (20 mL) and stirred at 25° C. for 4 hours. Tlc indicatedcomplete and clean reaction to the diol (Rf of starting to diol 0.40 to0.15 in dichloromethane/methanol 97:3 on silica). Potassium periodate(0.81 g, 3.56 mmol, 2.2 eq) was dissolved in water (10 mL) and added tothe reaction. After 17 hours the tlc indicated a 90% complete reaction(aldehyde Rf 0.35 in system noted above). The reaction solution wasfiltered, quenched with 5% aqueous sodium bisulfite (200 mL) and theproduct aldehyde was extracted with ethyl acetate (2×200 mL). Theorganic layers were combined, washed with brine (2×100 mL) andconcentrated to an oil. The oil was dissolved in absolute ethanol (15mL) and sodium borohydride (1 g) was added. After 2 hours at 25° C. thetlc indicated a complete reaction. Water (5 mL) was added to destroy theborohydride. After 2 hours the reaction was stripped and the residue waspartitioned between ethyl acetate and saturated sodium bicarbonatesolution (50 mL each). The organic layer was concentrated in vacuo andthe residue was columned (silica gel 30 g, dichloromethane-methanol97:3). The product containing fractions were combined and stripped anddried to 0.50 g (50%) of white foam. The NMR was consistent with that ofmaterial prepared by the glycosylation route.

EXAMPLE 50 2′-O-(2-Hydroxyethyl)-5-methyluridine

In a 100 mL stainless steel pressure reactor, ethylene glycol (20 mL)was slowly added to a solution of borane in tetrahydrofuran (1 M, 10 mL,10 mmol) with stirring. Hydrogen gas rapidly evolved. Once the rate ofbubbling subsided, 2,2′-anhydro-5-methyluridine (1.0 g, 0.4.2 mmol) andsodium bicarbonate (3 mg) were added and the reactor was sealed. Thereactor was placed in an oil bath and heated to 150° C. internaltemperature for 72 hours. The bomb was cooled to room temperature andopened. TLC revealed that 65% of the starting material was gone(starting material and product Rf 0.25 and 0.40 respectively in 4:1ethyl acetate/methanol on silica gel). The reaction was worked upincomplete. The crude solution was concentrated (1 mm Hg at 100° C.,coevaporated with methanol (50 mL), boiling water (15 mL) and absoluteethanol (2×25 mL) and the residue was dried to 1.3 g of off white foam(1 mm Hg, 25° C., 2 hours). MR of the crude product was consistent with65% desired product and 35% starting material. The TLC Rf matched (oncospot) the same product generated by treating the DMT derivative abovewith dilute hydrochloric acid in methanol as well as the Rf of one ofthe spots generated by treating a sample of this product withdimethoxytrityl chloride matched the known DMT derivative (other spotswere DMT on side chain and bis substituted product).

EXAMPLE 51N4-Benzoyl-2′-O-(2-phthalimido-N-oxyethyl)-51-O-(4,4′-dimethoxytrityl)cytidine-3′-[(2-cyanoethyl)-N,N-diisopropylphosphoramidite]

The 2′-O-aminooxyethyl cytidine and guanosine analogs may be preparedvia similar chemistry in combination with reported literatureprocedures. Key to the synthetic routes is the selective 2′-O-alkylationof unprotected nucleosides. (Guinosso, C. J., Hoke, G. D., Frier, S.,Martin, J. F., Ecker, D. J., Mirabelli, C. K., Crooke, S. T., Cook, P.D., Nucleosides Nucleotides, 1991, 10, 259; Manoharan, M., Guinosso, C.J., Cook, P. D., Tetrahedron Lett., 1991, 32, 7171; Izatt, R. M.,Hansen, L. D., Rytting, J. H., Christensen, J. J., J. Am. Chem. Soc.,1965, 87, 2760. Christensen, L. F., Broom, A. D., J. Org. Chem., 1972,37, 3398. Yano, J., Kan, L. S., Ts′o, P.O.P., Biochim. Biophys. Acta,1980, 629, 178; Takaku, H., Kamaike, K., Chemistry Lett. 1982, 189).Thus, cytidine may be selectively alkylated to afford the intermediate2′-O-(2-ethylacetyl)-cytidine. The 3′-isomer of2′-O-(2-ethylacetyl)cytidine is typically present in a minor amount andcan be resolved by chromatography or crystallization.2′-O-(2-ethylacetyl)-cytidine can be protected to give2′-O-(2-ethylacetyl)-5′-O-(4,4′-dimethoxytrityl)cytidine which uponreduction gives2′-O-(2-hydroxyethyl)-5′-O-(4,4′-dimethoxytrityl)cytidine.

This compound is further N-4-benzoylated, the primary hydroxyl group maybe displaced by N-hydroxyphthalimide via a Mitsunobu reaction, and theprotected nucleoside may be phosphitylated as usual to yieldN4-benzoyl-2′-O-(2-phthalimido-N-oxyethyl)-5′-O-(4,4′-dimethoxytrityl)cytidine-3′-[(2-cyanoethyl)-N,N-diisopropylphosphoramidite].

EXAMPLE 52N2-Isobutyryl-6-O-diphenylcarbamoyl-2′-O-(2-ethylacetyl)-5′-O-(4,4′-dimethoxytrityl)guanosine-3′-[(2-cyanoethyl)-N,N-diisopropylphosphoramidite]

In a similar fashion to the previous example the 2′-O-aminooxyethylguanosine analog may be obtained by selective 2′-O-alkylation ofdiaminopurine riboside (multigram quantities of diaminopurine ribosidemay be purchased from Schering AG (Berlin) to provide2′-O-(2-ethylacetyl)diaminopurine riboside along with a minor amount ofthe 3′-O-isomer. The 2′-O-(2-ethylacetyl)diaminopurine riboside isresolved and converted to 2′-O-(2-ethylacetyl)guanosine by treatmentwith adenosine deaminase. (McGee, D. P. C., Cook, P. D., Guinosso, C.J., PCT Int. Appl., 85 pp.; PIXXD2; WO 94/02501 A1 940203.) Standardprotection procedures should afford2′-O-(2-ethylacetyl)-5′-O-(4,4′-dimethoxytrityl)guanosine and2N-isobutyryl-6-O-diphenylcarbamoyl-2′-O-(2-ethylacetyl)-5′-O-(4,4′-dimethoxytrityl)guanosinewhich may be reduced to provide2-N-isobutyryl-6-O-diphenylcarbamoyl-2′-O-(2-ethylacetyl)-51-O-(4,4′-dimethoxytrityl)guanosine.As illustrated above the hydroxyl group may be displaced byN-hydroxyphthalimide via a Mitsunobu reaction, and the protectednucleoside may phosphitylated to yield2-N-isobutyryl-6-O-diphenylcarbamoyl-2′-O-(2-ethylacetyl)-5′-O-(4,4′-dimethoxytrityl)guanosine-3′-[(2-cyanoethyl)-N,N-diisopropylphosphoramidite].

EXAMPLES 53-85 Procedures for the Preparation of Compounds of theFormula:

wherein:

B is a heterocyclic base moiety and DMTr is dimethoxytrityl.

EXAMPLE 53 5′-O-tert-Butyldiphenylsilyl-O²-2′-anhydro-5-methyluridie

O²-2′-anhydro-5-methyluridine (Pro. Bio. Sint., Varese, Italy, 100.0 g,0.416 mmol), dimethylaminopyridine (0.66 g, 0.013 eq, 0.0054 mmol) weredissolved in dry pyridine (500 ml) at ambient temperature under an argonatmosphere and with mechanical stirring. tert-Butyldiphenylchlorosilane(125.8 g, 119.0 mL, 1.1 eq, 0.458 mmol) was added in one portion. Thereaction was stirred for 16 hours at ambient temperature. TLC (Rf 0.22,ethyl acetate) indicated a complete reaction. The solution wasconcentrated under reduced pressure to a thick oil. This was partitionedbetween dichloromethane (1 L) and sat′d sodium bicarbonate (2×1 L) andbrine (1 L). The organic layer was dried over sodium sulfate andconcentrated under reduced pressure to a thick oil. The oil wasdissolved in a 1:1 mixture of ethyl acetate and ethyl ether (600 mL) andthe solution was cooled to −10° C. The resulting crystalline product wascollected by filtration, washed with ethyl ether (3×200 mL) and dried(40° C., 1 mm Hg, 24 h) to 149 g (74.8%) of white solid. TLC and NMRwere consistent with pure product.

EXAMPLE 545′-O-tert-Butyldiphenylsilyl-2′-O-(2-hydroxyethyl)-5-methyluridine

In a 2 L stainless steel, unstirred pressure reactor as added borane intetrahydrofuran (1.0 M, 2.0 eq, 622 mL). In the fume hood and withmanual stirring, ethylene glycol (350 mL, excess) was added cautiouslyat first until the volution of hydrogen gas subsided.5′-O-tert-butyldiphenylsilyl-O²-2′-anhydro-5-methyluridine (149 g, 0.311mol) and sodium bicarbonate (0.074 g, 0.003 eq) were added with manualstirring. The reactor was sealed and heated in an oil bath until aninternal temperature of 160° C. was reached and then maintained for 16hours (pressure <100 psig). The reaction vessel was cooled to ambientand opened. TLC (Rf 0.67 for desired product and Rf 0.82 for ara-T sideproduct, ethyl acetate) indicated about 70% conversion to the product.In order to avoid additional side product formation, the reaction wasstopped, concentrated under reduced pressure (10 to 1 mm Hg) in a warmwater bath (40-100° C.) with the more extreme conditions used to removethe ethylene glycol. [Alternatively, once the low boiling solvent isgone, the remaining solution can be partitioned between ethyl acetateand water. The product will be in the organic phase.] The residue waspurified by column chromatography (2 kg silica gel, ethylacetate-hexanes gradient 1:1 to 4:1). The appropriate fractions werecombined, stripped and dried to product as a white crisp foam (84 g,50%), contaminated starting material (17.4 g) and pure reusable startingmaterial 20 g. The yield based on starting material less pure recoveredstarting material was 58%. TLC and NMR were consistent with 99% pureproduct.

NMR (DMSO-d6) d 1.05 (s, 9H, t-butyl), 1.45 (s, 3 H, CH3), 3.5-4.1 (m, 8H, CH2CH2, 3′-H, 4′-H, 5′-H, 5″-H), 4.25 (m, 1 H, 2′-H), 4.80 (t, 1 H,CH2O-H), 5.18 (d, 2H, 3′-OH), 5.95 (d, 1 H, 1′-H), 7.35-7.75 (m, 11 H,Ph and C6-H), 11.42 (s, 1 H, N-H).

EXAMPLE 552′-O-([2-Phthalimidoxy)ethyl]-5′-t-butyldiphenylsilyl-5-methyluridine

Nucleoside5′-O-tert-butyldiphenylsilyl-2′-O-(2-hydroxyethyl)-5-methyluridine (20g, 36.98 mmol) was mixed 5 with triphenylphosphine (11.63 g, 44.36 mmol)and N-hydroxyphthalimide (7.24 g, 44.36 mmol). It was then dried overP₂O₅ under high vacuum for two days at 40° C. The reaction mixture wasflushed with argon and dry THF (369.8 mL, Aldrich, sure seal bottle) wasadded to get a clear solution. Diethyl-azodicarboxylate (6.98 mL, 44.36mmol) was added dropwise to the reaction mixture. The rate of additionis maintained such that resulting deep red coloration is just dischargedbefore adding the next drop. After the addition was complete, thereaction was stirred for 4 hrs. By that time TLC showed the completionof the reaction (ethylacetate:hexane, 60:40). The solvent was evaporatedin vacuum. Residue obtained was placed on a flash column and eluted withethyl acetate:hexane (60:40), to get the title compound as white foam(21.819, 86%). Rf 0.56 (ethyl acetate:hexane, 60:40). MS (FAB⁻)m/e 684(M−H⁺).

EXAMPLE 565′-O-tert-Butyldiphenylsilyl-2′-O-[(2-formadoximinooxy)ethyl]-5-methyluridine

2′-O-([2-Phthalimidoxy)ethyl]-5′-t-butyldiphenylsilyl-5-methyluridine(3.1 g, 4.5 mmol) was dissolved in dry CH₂Cl₂ (4.5 mL) andmethylhydrazine (300 mL, 4.64 mmol) was added dropwise at −10° C. to 0°C. After 1 hr the mixture was filtered, the filtrate was washed with icecold CH₂Cl₂ and the combined organic phase was washed with water, brineand 30 dried over anhydrous Na₂SO₄. The solution concentrated to get2′-O-(aminooxyethyl) thymidine, which was then dissolved in MeOH (67.5mL). To this formaldehyde (20% aqueous solution, w/w, 1.1 eg.) was addedand the mixture for 1 hr.

Solvent removed under vacuum; residue chromatographed to get 35 thetitle compound as white foam (1.95, 78%). Rf 0.32 (5% MeOH in CH₂Cl₂).MS (Electrospray⁻) m/e 566 (M−H^(⊕)).

EXAMPLE 575′-O-tert-Butyldiphenylsilyl-2′-O-[N,N-dimethylaminooxyethyl]-5-methyluridine

5′-O-tert-Butyldiphenylsilyl-2′-O-[(2-formadoximinooxy)ethyl]-5-methyluridine(1.77 g, 3.12 mmol) was dissolved in a solution of 1M pyridiniump-toluenesulfonate (PPTS) in dry MeOH (30.6 mL). Sodiumcyanoborohydride(0.39 g, 6.13 mmol) was added to this solution at 10° C. under inertatmosphere. The reaction mixture was stirred for 10 minutes at 10° C.After that the reaction vessel was removed from the ice bath and stirredat room temperature for 2 hr, the reacticn monitored by TLC (5% MeOH inCH₂Cl₂). Aqueous NaHCO₃ solution (5%, l0 mL) was added and extractedwith ethyl acetate (2×20 mL). Ethyl acetate phase dried over anhydrousNa₂SO₄, evaporated to dryness. Residue dissolved in a solution of 1MPPTS in MeOH (30.6 mL). Formaldehyde (20% w/w, 30 mL, 3.37 mmol) wasadded and the reaction mixture was stirred at room temperature for 10minutes. Reaction mixture cooled to 10° C. in an ice bath,sodiumcyanoborohydride (0.39 g, 6.13 mmol) was added and reactionmixture stirred at 10° C. for 10 minutes. After 10 minutes, the reactionmixture was removed from the ice bath and stirred at room temperaturefor 2 hrs. To the reaction mixture 5% NaHCO₃ (25 mL) solution was addedand extracted with ethyl acetate (2×25 mL). Ethyl acetate layer wasdried over anhydrous Na₂SO₄; and evaporated to dryness. The residueobtained was purified by flash column chromatography and eluted with 5%MeOH in CH₂Cl₂ to get the title compound as a white foam (14.6 g, 80%).Rf 0.35 (5% MeOH in CH₂Cl₂) MS (FAB^(⊕)) m/e 584 (M+H^(⊕)).

EXAMPLE 58 2′-O-(Dimethylaminooxyethyl)-5-methyluridine

Triethylamine trihydrofluoride (3.91 mL, 24.0 mmol) was issolved in dryTHF and triethylamine (1.67 mL, 12 mmol, dry, ept over KOH). Thismixture of triethylamine-2HF was then added to5′-O-tert-butyldiphenylsilyl-2′-O-[N,N-dimethylaminooxyethyl]-5-methyluridine(1.40 g, 2.4 mmol) and stirred at room temperature for 24 hrs. Reactionwas monitored by TLC (5% MeOH in CH₂Cl₂). Solvent removed under vacuumand the residue placed on a flash column and eluted with 10% MeOH inCH₂Cl₂ to get the title compound (766 mg, 92.5%). Rf 0.27 (5% MeOH inCH₂Cl₂). MS (FAB^(⊕)) m/e 346 (M+H^(⊕)).

EXAMPLE 59 5′-O-DMT-2′-O-(Dimethylaminooxyethyl)-5-methyluridine

2′-O-(dimethylaminooxyethyl)-5-methyluridine (750 mg, 2.17 mmol) wasdried over P₂O₅ under high vacuum overnight at 40° C. It was thenco-evaporated with anhydrous pyridine (20 mL). The residue obtained wasdissolved in pyridine (llmL) under argon atmosphere.4-dimethylaminopyridine (26.5 mg, 2.60 mmol), 4,4′-dimethoxytritylchloride (880 mg, 2.60 mmol) was added to the mixture and the reactionmixture was stirred at room temperature until all of the startingmaterial disappeared. Pyridine was removed under vacuum and the residuechromatographed and eluted with 10% MeOH in CH₂Cl₂ (containing a fewdrops of pyridine) to get the title compound (1.13 g, 80%). Rf 0.44((10% MeOH in CH₂Cl₂). MS (FAB^(⊕)) m/e 648 (M+H^(⊕)).

EXAMPLE 605′-O-DMT-2′-O-(2-N,N-Dimethylaminooxyethyl)-5-methyluridine-3′-[(2-cyanoethyl)-N,N-diisopropylphosphoramidite]

5′-O-DMT-2′-O-(dimethylaminooxyethyl)-5-methyluridine (1.08 g, 1.67mmol) was co-evaporated with toluene (20 mL). To the residueN,N-diisopropylamine tetrazonide (0.29 g, 1.67 mmol) was added and driedover P₂O₅ under high vacuum overnight at 40° C. Then the reactionmixture was dissolved in anhydrous acetonitrile (8.4 mL) and2-cyanoethyl-N,N,N¹,N¹-tetraisopropylphosphoramidite (2.12 mL, 6.08mmol) was added. The reaction mixture was stirred at ambient temperaturefor 4 hrs under inert atmosphere. The progress of the reaction wasmonitored by TLC (hexane:ethyl acetate 1:1). The solvent was evaporated,then the residue was dissolved in ethyl acetate (70 mL) and washed with5% aqueous NaHCO₃ (40 mL). Ethyl acetate layer was dried over anhydrousNa₂SO₄ and concentrated. Residue obtained was chromatographed (ethylacetate as eluent) to get the title compound as a foam (1.04 g, 74.9%).Rf 0.25 (ethyl acetate:hexane, 1:1).

³¹P NMR (CDCl₃) δ 150.8 ppm; MS (FAB^(⊕)) m/e 848 (M+H^(⊕)).

EXAMPLE 61 2′/3′-O-Allyl Adenosine

Adenosine (20 g, 74.84 mmol) was dried over P₂O₅ under high vacuum at40° C. for two days. It was then suspended in DMF under inertatmosphere. Sodium hydride (2.5 g, 74.84 mmol, 60% dispersion in mineraloil), stirred at. room temperature for 10 minutes. Then allyl bromide(7.14 mL, 82.45 mmol) was added dropwise and the reaction mixture wasstirred at room temperature overnight. DMF was removed under vacuum andresidue was washed with ethyl acetate (100 mL). Ethyl acetate layer wasdecanted. Filtrate obtained contained product. It was then placed on aflash column and eluted with 10% MeOH in CH₂Cl₂ to get the titlecompound (15.19 g, 66%). Rf 0.4, 0.4a ((10% MeOH in CH₂Cl₂).

EXAMPLE 62 2′/3′-O-Allyl-N⁶-benzoyl Adenosine

2′/3′-O-allyl adenosine (15.19 g, 51.1 mmol) was dried over P₂O₅ underhigh vacuum overnight at 40° C. It was then dissolved in anhydrouspyridine (504.6 mL) under inert atmosphere. Trimethylchlorosilane (32.02mL, 252.3 mmol) was added at 0° C. and the reaction mixture was stirredfor 1 hr under inert atmosphere. Then benzoyl chloride (29.4 mL, 252.3mmol) was added dropwise. once the addition of benzoyl chloride wasover, the reaction mixture was brought to room temperature and stirredfor 4 hrs. Then the reaction mixture was brought to 0° C. in an icebath. Water (10.9 mL) was added and the reaction mixture was stirred for30 minutes. Then NH₄OH (100.0 mL, 30% aqueous solution w/w) was added,keeping the reaction mixture at 0° C. and stirring for an additional 1hr. Solvent evaporated residue partitioned between water and ether.Product precipitates as an oil, which was then chromatographed (5% MeOHin CH₂Cl₂) to get the title compound as a white foam (12.67 g, 62%).

EXAMPLE 63 3′-O-Allyl-5′-O-tert-butyldiphenylsilyl-N⁶-benzoyl-adenosine

2′/3′-O-allyl-N⁶-benzoyl adenosine (11.17 g, 27.84 mmol) was dried overP₂O₅ under vacuum at 40° C., then dissolved in dry CH₂Cl₂ (56 mL, sureseal from Aldrich). 4-dimethylaminopyridine (0.34 g, 2.8 mmol),triethylamine (23.82 mL, 167 mmol) and t-butyldiphenylsilyl chloridewere added. The reaction mixture was stirred vigorously for 12 hr.Reaction was monitored by TLC (ethyl acetate:hexane 1:1). It was thendiluted with CH₂Cl₂ (50 mL) and washed with water (3×30 mL).Dichloromethane layer was dried over anhydrous Na₂SO₄ and evaporated todryness. Residue purified by flash chromatography (ethyl acetate:hexane1:1 as eluent) to get the title compound as a white foam (8.85 g, 49%).Rf 0.35 (ethyl acetate:hexane, 1:1).

EXAMPLE 645′-O-tert-Butyldiphenylsilyl-N⁶-benzoyl-2′-O-(2,3-dihydroxypropyl)-adenosine

2,3-O-allyl-5′-O-tert-butyldiphenylsilyl-N⁶-benzoyl-adenosine (5.5 g,8.46 mmol), 4-methylmorpholine N-oxide (1.43 g, 12.18 mmol) weredissolved in dioxane (45.42 mL). 4% aqueous solution of OSO₄ (1.99 mL,0.31 mmol) was added. The reaction mixture was protected from light andstirred for 3 hrs. Reaction was monitored by TLC (5% MeOH in CH₂Cl₂).Ethyl acetate (100 mL) was added and the resulting reaction mixture waswashed with water (1×50 mL). Ethyl acetate layer was dried overanhydrous Na₂SO₄ and evaporated to get the title compound (5.9 g) andused for next step without purification. Rf 0.17 (5% MeOH in CH₂Cl₂).

EXAMPLE 655′-O-tert-Butyldiphenylsilyl-N⁶-benzoyl-2′-O-(formylmethyl)-adenosine

5′-O-tert-butyldiphenylsilyl-N⁶-benzoyl-2′-O-(2,3-dihydroxypropyl)-adenosine(5.59 g, 8.17 mmol) was dissolved in dry CH₂Cl₂ (40.42 mL). To thisNaIO₄ adsorbed on silica gel (Ref. J. Org. Chem. 1997, 62, 2622-2624)(16.34 g, 2 g/mmol) was added and stirred at ambient temperature for 30minutes. Reaction monitored by TLC (5% MeOH in CH₂Cl₂). Reaction mixturewas filtered and the filtrate washed thoroughly with CH₂Cl₂.Dichloromethane layer evaporated to get the title compound (5.60 g) thatwas used in the next step without purification. Rf 0.3 (5% MeOH inCH₂Cl₂).

EXAMPLE 665′-O-tert-Butyldiphenylsilyl-N⁶-2′-O-(2-hydroxyethyl)adenosine

5′-O-tert-butyldiphenylsilyl-N⁶-benzoyl-2′-O-(formylmethyl)-adenosine(5.55 g, 8.50 mmol) was dissolved in a solution of 1M pyridiniump-toluenesulfonate in anhydrous MeOH (85 mL). Reaction mixture wasprotected from moisture.

Sodiumcyanoborohydride (1.08 g, 17.27 mmol) was added and reactionmixture stirred at ambient temperature for 5 hrs.

The progress of the reaction was monitored by TLC (5% MeOH in CH₂Cl₂).The reaction mixture was diluted with ethyl acetate (150 mL), thenwashed with 5% NaHCO₃ (75 mL) and brine (75 mL). Ethyl acetate layer wasdried over anhydrous Na₂SO₄ and evaporated to dryness. Residue purifiedby flash chromatography (5% MeOH in CH₂Cl₂) to get the title compound(4.31 g, 77.8%). Rf 0.21 (5% MeOH in CH₂Cl₂). MS (FAB^(⊕)) m/e 655(M+H^(⊕)), 677 (M+Na^(⊕)).

EXAMPLE 675′-tert-Butyldiphenylsilyl-N6-benzoyl-2′-O-(2-phthalimidooxyethyl)adenosine

5′-tert-butyldiphenylsilyl-N6-benzoyl-2-O-(formylmethyl)-adenosine (3.22g, 4.92 mmol) was mixed with triphenylphosphine (1.55 g, 5.90 mmol) andN-hydroxyphthalimide (0.96 g, 5.90 mmol). It was then dried over P₂O₅under vacuum at 40° C. for two days. Dissolved dried mixture inanhydrous THF (49.2 mL) under inert atmosphere. Diethyl azodicarboxylate(0.93 mL, 5.90 mmol) was added dropwise. The rate of addition wasmaintained such that resulting deep red coloration is just dischargedbefore adding the next drop. After the addition was completed, thereaction was stirred for 4 hrs, monitored by TLC (ethylacetate:hexane70:30). Solvent was removed under vacuum and the residue dissolved inethyl acetate (75 mL). The ethyl acetate layer was washed with water (75mL), then dried over Na₂SO₄, concentrated and chromatographed(ethylacetate:hexane 70:30) to get the title compound (3.60 g, 91.5%).Rf 0.27 ethyl acetate:hexane, 7:3) MS (FAB^(⊕)) m/e 799 (M+H^(⊕)), 821(M+Na^(⊕)).

EXAMPLE 685′-O-tert-Butyldiphenylsilyl-N⁶-benzoyl-2′-O-(2-formaldoximinooxyethyl)adenosine

5′-tert-Butyldiphenylsilyl-N⁶-benzoyl-2′-O-(2-phthalimidooxyethyl)adenosine(3.5 g, 4.28 mmol) was dissolved in CH₂Cl₂ (43.8 mL). N-methylhydrazine(0.28 mL, 5.27 mmol) was added at −10° C. and the reaction mixture wasstirred for 1 hr at −10 to 0° C. Reaction monitored by TLC (5% MeOH inCH₂Cl₂). A white precipitate formed was filtered and filtrate washedwith ice cold CH₂Cl₂ thoroughly. Dichloromethane layer evaporated on arotavapor keeping the water bath temperature of rotavapor at less than25° C. Residue obtained was then dissolved in MeOH (65.7 mL).Formaldehyde (710 mL, 4.8 mmol, 20% solution in water) was added and thereaction mixture was stirred at ambient temperature for 1 hr. Reactionmonitored by ¹H NMR. Reaction mixture concentrated and chromatographed(5% MeOH in CH₂Cl₂) to get the title compound as a white foam (2.47 g,83%). Rf 0.37 (5% MeOH in CH₂Cl₂) MS (FAB^(⊕)) m/e 681 (M+H^(⊕)).

EXAMPLE 695′-tert-Butyldiphenylsilyl-N⁶-benzoyl-2′-O-(2-N,N-dimethylaminooxyethyl)adenosine

5-O-tert-butyldiphenylsilyl-N⁶-benzoyl-2′-O-(2-formaldoximinooxyethyl)adenosine(2.2 g, 3.23 mmol) was dissolved in a solution of 1M pyridiniump-toluenesulfonate (PPTS) in MeOH (32 mL). Reaction protected frommoisture.

Sodium cyanoborohydride (0.31 g) was added at 10° C. and reactionmixture was stirred for 10 minutes at 10° C. It was then brought toambient temperature and stirred for 2 hrs, monitored by TLC (5% MeOH inCH₂Cl₂). 5% aqueous sodiumbicarbonate (100 mL) and extracted with ethylacetate (3×50 mL). Ethyl acetate layer was dried over anhydrous Na₂SO₄and evaporated to dryness. Residue was dissolved in a solution of 1MPPTS in MeOH (32 mL). Formaldehyde (0.54 mL, 3.55 mmol, 20% aqueoussolution) was added and stirred at room temperature for 10 minutes.Sodium cyanoborohydride (0.31 g) was added at 10° C. and stirred for 10minutes at 10° C.

Then the reaction mixture was removed from ice bath and stirred at roomtemperature for an additional 2 hrs, monitored by TLC (5% MeOH inCH₂Cl₂). Reaction mixture was diluted with 5% aqueous NaHCO₃ (100 mL)and extracted with ethyl acetate (3×50 mL). Ethyl acetate layer wasdried, evaporated and chromatographed (5% MeOH in CH₂Cl₂) to get thetitle compound (1.9 g, 81.8%). Rf 0.29 (5% MeOH in CH₂Cl₂). MS (FAB^(⊕))m/e 697 (M+H^(⊕)), 719 (M+Na^(⊕)).

EXAMPLE 70 N⁶-Benzoyl-2′-O-(N,N-dimethylaminooxyethyl)adenosine

To a solution of Et₃N-3HF (1.6 g, 10 mmol) in anhydrous THF (10 mL)triethylamine (0.71 mL, 5.12 mmol) was added. Then this mixture wasadded to5′-tert-butyldiphenylsilyl-N⁶-benzoyl-2′-O-(2-N,N-dimethylaminooxyethyl)adenosine(0.72 g, 1 mmol) and stirred at room temperature under inert atmospherefor 24 hrs. Reaction monitored by TLC (10% MeOH in CH₂Cl₂). Solventremoved under vacuum and the residue chromatographed (10% MeOH inCH₂Cl₂) to get the title compound (0.409 g, 89%). Rf 0.40 (10% MeOH inCH₂Cl₂). MS (FAB^(⊕)) m/e 459 (M+H^(⊕)).

EXAMPLE 715′-O-Dimethoxytrityl-N⁶-benzoyl-2-O-(2-N,N-dimethylaminooxyethyl)adenosine

N⁶-benzoyl-2′-O-(N,N-dimethylaminooxyethyl)adenosine (0.4 g, 0.87 mmol)was dried over P₂O₅ under vacuum overnight at 40° C.4-dimethylaminopyridine (0.022 g, 0.17 mmol) was added. Then it wasco-evaporated with anhydrous pyridine (9 mL). Residue was dissolved inanhydrous pyridine (2 mL) under inert atmosphere, and4,4′-dimethoxytrityl chloride (0.58 g, 1.72 mmol) was added and stirredat room temperature for 4 hrs. TLC (5% MeOH in CH₂Cl₂) showed thecompletion of the reaction. Pyridine was removed under vacuum, residuedissolved in CH₂Cl₂ (50 mL) and washed with aqueous 5% NaHCO₃ (30 mL)solution followed by brine (30 mL). CH₂Cl₂ layer dried over anhydrousNa₂SO₄ and evaporated. Residue chromatographed (5% MeOH in CH₂Cl₂containing a few drops of pyridine) to get the title compound (0.5 g,75%). Rf 0.20 (5% MeOH in CH₂Cl₂). MS (Electrospray⁻) m/e 759 (M+H^(⊕)).

EXAMPLE 72N⁶-Benzoyl-5′-O-DMT-2′-O-(N,N-dimethylaminooxyethyl)adenosine-3′-O-phosphoramidite

N⁶-benzoyl-2′-O-(N,N-dimethylaminooxyethyl)adenosine (0.47 g, 0.62 mmol)was co-evaporated with toluene (5 mL). Residue was mixed withN,N-diisopropylamine tetrazolicle (0.106 g, 0.62 mmol) and dried overP₂O₅ under high vacuum overnight. Then it was dissolved in anhydrousCH₃CN (3.2 mL) under inert atmosphere. 2-cyanoethyl-tetraisopropylphosphordiamidite (0.79 mL, 2.48 mmol) was added dropwise and thereaction mixture was stirred at room temperature under inert atmospherefor 6 hrs. Reaction was monitored by TLC (ethyl acetate containing a fewdrops of pyridine). Solvent was removed, then residue was dissolved inethyl acetate (50 mL) and washed with 5% aqueous NaHCO₃ (2×25 mL). Ethylacetate layer was dried over anhydrous Na₂SO₄, evaporated, and residuechromatographed (ethyl acetate containing a few drops of pyridine) toget the title compound (0.45 g, 76%). MS (Electrospray⁻) m/e 959(M+H^(⊕)). ³¹P NMR (CDCl₃) δ 151.36, 150.77 ppm.

EXAMPLE 73 2′/3′-O-Allyl-2,6-diaminopurine Riboside

2,6-Diaminopurine riboside (30 g, 106.4 mmol) was suspended in anhydrousDMF (540 mL). Reaction vessel was flushed with argon. Sodium hydride(3.6 g, 106.4 mmol, 60% dispersion in mineral oil) was added and thereaction stirred for 10 min. Allyl bromide (14.14 mL, 117.22 mmol) wasadded dropwise over 20 min. The resulting reaction mixture stirred atroom temperature for 20 hr. TLC (10% MeOH in CH₂Cl₂) showed completedisappearance of starting material. DMF was removed under vacuum and theresidue absorbed on silica was placed on a flash column and eluted with10% MeOH in CH₂Cl₂. Fractions containing mixture of 2′ and 3′ allylatedproduct was pooled together and concentrated to dryness to yield amixture of the title compounds (26.38 g, 77%). Rf 0.26, 0.4 (10% MeOH inCH₂Cl₂).

EXAMPLE 74 2′-O-Allyl-guanosine

A mixture of 2′/3′-O-allyl-2,6-diaminopurine riboside (20 g, 62.12 mmol)was suspended in 100 mm sodium phosphate buffer (pH 7.5) and adenosinedeaminase (1 g) was added. The resulting solution was stirred veryslowly for 60 hr, keeping the reaction vessel open to atmosphere.Reaction mixture was then cooled in ice bath for one hr and theprecipitate obtained was filtered, dried over P₂O₅ under high vacuum toyield the title compound as white powder (13.92 g, 69.6% yield). Rf 0.19(20% MeOH in CH₂Cl₂).

EXAMPLE 75 2′-O-Allyl-3′,5′-bis(tert-butyldiphenylsilyl)guanosine

2′-O-allyl-guanosine (6 g, 18.69 mmol) was mixed with imidazole (10.18g, 14.952 mmol) and was dried over P₂O₅ under high vacuum overnight. Itwas then flushed with argon. Anhydrous DMF (50 mL) was added and stirredwith the reaction mixture for 10 minutes. To thistert-butyldiphenylsilyl chloride (19.44 mL, 74.76 mmol) was added andthe reaction mixture stirred overnight under argon atmosphere. DMF wasremoved under vacuum and the residue was dissolved in ethyl acetate (100mL) and washed with water (2×75 mL). Ethyl acetate layer was dried overanhydrous Na₂SO₄ and evaporated to dryness. Residue placed on a flashcolumn and eluted with 5% MeOH in CH₂Cl₂. Fractions containing theproduct were pooled together and evaporated to give the title compound(10.84 g, 72% yield) as a white foam. Rf=? MS (FAB^(⊕)) m/e 800(M+H^(⊕)), 822 (M+Na^(⊕)).

EXAMPLE 762′-O-(2-Hydroxyethyl)-3′,5′-bis(tert-butyldiphenylsilyl)guanosine

2′-O-allyl-3′,5′-bis(tert-butyldiphenylsilyl)guanosine (9 g, 11.23 mmol)was dissolved in CH₂Cl₂ (80 mL). To the clear solution acetone (50 mL),4-methyl morpholine-N-oxide (1.89 g, 16.17 mmol) was added. The reactionflask was protected from light. Thus 4% aqueous solution of osmiumtetroxide was added and the reaction mixture was stirred at roomtemperature for 6 hr. Reaction volume was concentrated to half and ethylacetate (50 mL) was added. It was then washed with water (30 mL) andbrine (30 mL). Ethyl acetate layer was dried over anhydrous Na₂SO₄ andevaporated to dryness. Residue was then dissolved in CH₂Cl₂ and NaIO₄adsorbed on silica (21.17 g, 2 g/mmol) was added and stirred with thereaction mixture for 30 min. The reaction mixture was filtered andsilica was washed thoroughly with CH₂Cl₂. Combined CH₂Cl₂ layer wasevaporated to dryness. Residue was then dissolved in dissolved in 1Mpyridinium-p-toluene 15 sulfonate (PPTS) in dry MeOH (99.5 mL) underinert atmosphere. To the clear solution sodium cyanoborohydride (1.14 g,18.2 mmol) was added and stirred at room temperature for 4 hr. 5%aqueous sodium bicarbonate (50 mL) was added to the reaction mixtureslowly and extracted with ethyl acetate (2×50 mL). Ethyl acetate layerwas dried over anhydrous Na₂SO₄ and evaporated to dryness. Residueplaced on a flash column and eluted with 10% MeOH in CH₂Cl₂ to givet thetitle compound (6.46 g, 72% yield). MS (Electrospray−) m/e 802(M−H^(⊕)).

EXAMPLE 772′-O-[(2-Phthalimidoxy)ethyl]-3′,5′-bis(tertbutyldiphenylsilyl)guanosine

2′-O-(2-hydroxyethyl)-3′,5′-bis(tert-butyldiphenylsilyl)guanosine (3.7g, 4.61 mmol) was mixed with Ph₃P (1.40 g, 5.35 mmol), and hydroxyphthalimide (0.87 g, 5.35 mmol). It was then dried over P₂O₅ under highvacuum for two days at 40° C. These anhydrous THF (46.1 mmol) was addedto get a clear solution under inert atmosphere.

Diethylazidocarboxylate (0.73 mL, 4.61 mmol) was added dropwise in sucha manner that red color disappears before addition of the next drop.Resulting solution was then stirred at room temperature for 4 hr. THFwas removed under vacuum and the residue dissolved in ethyl acetate (75mL) and washed with water (2×50 mL). Ethyl acetate layer was dried overanhydrous Na₂SO₄ and concentrated to dryness. Residue was purified bycolumn chromatography and eluted with 7% MeOH in ethyl acetate to givethe title compound (2.62 g, 60% yield). Rf 0.48 (10% MeOH in CH₂Cl₂). MS(FAB⁻) m/e 947 (M−H^(⊕)).

EXAMPLE 785′-O-DMT-2′-O-(N,N-Dimethylaminooxyethyl)-N2-isobutyrylguanosine-3′-O-phosphoramidite

2′-O-(2-phthalimido-N-oxyethyl)-3′,5′-O-bis-tert-butyldiphenylsilylguanosine (3.66 g, 3.86 mmol) was dissolved in anhydrous pyridine (40mL), the solution was cooled to 5° C., and isobutyryl chloride (0.808mL, 7.72 mmol) was added dropwise. The reaction mixture was allowed towarm to 25° C., and after 2 h additional isobutyryl chloride (0.40 mL,3.35 mmol) was added at 25° C. After 1 h the solvent was evaporated invaccuo (0.1 torr) at 30° C. to give a foam which was dissolved in ethylacetate (150 mL) to give a fine suspension. The suspension was washedwith water (2×15 mL) and brine (4 mL), and the organic layer wasseparated and dried over MgSO₄. The solvent was evaporated in vaccuo togive a foam, which was purified by column chromatography usingCH₂Cl₂-MeOH, 94:6, v/v, to afford the 5′-, 3′-O—, and N2-protectednucleoside as a white foam (2.57 g, 65%).

¹H NMR (CDCl₃): d 11.97 (br s, 1H), 8.73 (s, 1H), 7.8-7.2 (m, 25H), 5.93(d, 1H, J_(1′,2′)=3.3 Hz), 4.46 (m, 1H), 4.24 (m, 2H), 3.83 (m, 2H),3.60 (m, 2H), 3.32 (m, 1H), 2.67 (m, 1H), 1.30 (d, 3H, J=3.2 Hz), 1.26(d, 3H, J=3.1 Hz), 1.05 (s, 9H), 1.02 (s, 9H).

The 5′-O—, 3′-O—, and N2-protected nucleoside was further derivatizedinto the corresponding phosphoramidite using the chemistries describedabove for the A and T analogs to give the title compound.

EXAMPLE 793′-O-Acetyl-2′-O-(2-N,N-dimethylaminooxyethyl)-5′-O-tert-utyldiphenylsilylThymidine

5′-O-tert-butyldiphenylsilyl-2′-O-[N,N-dimethylaminooxyethyl]-5-methyluridine(3.04 g, 5.21 mmol) was dissolved in chloroform (11.4 mL). To this wasadded dimethylaminopyridine (0.99 g, 8.10 mmol) and the reaction mixturewas stirred for 10 minutes. Acetic anhydride (0.701 g, 6.87 mmol) wasadded and the reaction mixture was stirred overnight. The reactionmixture was then diluted with CH₂Cl₂ (40 mL) and washed with saturatedNaHCO₃ (30 mL) and brine (30 mL). CH₂Cl₂ layer evaporated to dryness.Residue placed on a flash column and eluted with ethyl acetate: hexane(80:20) to yield the title compound. Rf 0.43 (ethyl acetate:hexane,80:20). MS (Electrospray) m/e 624 (M−H^(⊕)).

EXAMPLE 802′-O-(2-N,N-Dimethylaminooxyethyl)-5′-O-tert-butyldiphenylsilyl 5-MethylCytidine

A suspension of 1,2,4-triazole (5.86 g, 84.83 mmol) in anhydrous CH₃CN(49 mL) was cooled in an ice bath for 5 to 10 min. under argonatmosphere. To this cold suspension POCl₃ (1.87 mL, 20 mmol) was addedslowly over 10 min. and stirring continued for an additional 5 min.Triethylamine (13.91 mL, 99.8 mmol) was added slowly over 30 min.,keeping the bath temperature around 0-2° C. After the addition wascomplete the reaction mixture was stirred at this temperature for anadditional 30 minutes when N-1-Hydroxyphthalimido-5-O-(cyanoethoxydiisopropylaminophosphoroamidite)-6-O-dimethyoxytrityl-5,6hexane-diol (3.12 g, 4.99 mmol) was added in anhydrous acetonitrile (3mL) in one portion. The reaction mixture was stirred at 0-2° C. for 10min. Then ice bath was removed and the reaction mixture was stirred atroom temperature for 1.5 hr. The reaction mixture was cooled to ° C. andthis was concentrated to smaller volume and dissolved in ethyl acetate(100 mL), washed with water (2×30 mL) and brine (30 mL). Organic layerwas dried over anhydrous Na₂SO₄ and concentrated to dryness. Residueobtained was then dissolved in saturated solution of NH₃ in dioxane (25mL) and stirred at room temperature overnight. Solvent was removed undervacuum. The residue was purified by column chromatography and elutedwith 10% MeOH in CH₂Cl₂ to give the title compound.

EXAMPLE 812′-O-(2,N,N-Dimethylaminooxyethyl)-N⁴-benzoyl-5′-O-tert-butyldiphenylsilylcytidine

2′-O-(2-N,N-dimethylaminooxyethyl)-5′-O-tert-butyldiphenylsilyl 5-methylcytidine (2.8 g, 4.81 mmol) was dissolved in anhydrous DMF (12.33 mL).Benzoic anhydride (1.4 g, 6.17 mmol) was added and the reaction mixturewas stirred at room temperature overnight. Methanol was added (1 mL) andsolvent evaporated to dryness. Residue was dissolved in dichloromethane(50 mL) and washed with saturated solution of NaHCO₃ (2×30 mL) followedby brine (30 mL). Dichloromethane layer was dried over anhydrous Na₂SO₄and concentrated. The residue obtained was purified by columnchromatography and eluted with 5% MeOH in CH₂Cl₂ to give the titlecompound as a foam.

EXAMPLE 82N⁴-Benzoyl-2′-O-(2-N,N-dimethylaminooxyethyl)-5-methylcytidine

2′-O-(2,N,N-dimethylaminooxyethyl)-N⁴-benzoyl-5′-O-tert-butyldiphenylsilylcytidine(2.5 g, 3.9 mmol) was dried over P₂O₅ under high vacuum. In a 100 mLround bottom flask, triethylamine trihydrofluoride (6.36 mL, 39 mmol) isdissolved in anhydrous THF (39 mL). To this, triethylamine (2.72 mL,19.5 mmol) was added and the mixture was quickly poured into2′-O-(2,N,N-dimethylaminooxyethyl)-N⁴-benzoyl-5′-O-tert-butyldiphenylsilylcytidineand stirred at room temperature overnight. Solvent is removed undervacuum and the residue kept in a flash column and eluted with 10% MeOHin CH₂Cl₂ to give the title compound.

EXAMPLE 83N⁴-Benzoyl-2′-O-(2-N,N-dimethylaminooxyethyl)-5-O′-dimetoxytrityl-5-methylcytidine

N⁴-Benzoyl-2′-O-(2-N,N-dimethylaminooxyethyl)-5-methylcytidine (1.3 g,2.98 mmol) was dried over P₂O₅ under high vacuum overnight. It was thenco-evaporated with anhydrous pyridine (10 mL). Residue was dissolved inanhydrous pyridine (15 mL), 4-dimethylamino pyridine (10.9 mg, 0.3 mmol)was added and the solution was stirred at room temperature under argonatmosphere for 4 hr. Pyridine was removed under vacuum and the residuedissolved in ethyl acetate and washed with 5% NaHCO₃ (20 mL) and brine(20 mL). Ethyl acetate layer was dried over anhydrous Na₂SO₄ andconcentrated to dryness. Residue was placed on a flash column and elutedwith 10% MeOH in CH₂Cl₂ containing a few drops of pyridine to give thetitle compound.

EXAMPLE 84N⁴-Benzoyl-2′-O-(2-N,N-dimethylaminooxyethyl)-5-dimethoxytrityl-5-methylcytidine-3′-O-phosphoramidite

N⁴-Benzoyl-2′-O-(2-N,N-dimethylaminooxyethyl)-5-O′-dimetoxytrityl-5-methylcytidine(1.54 g, 2.09 mmol) was co-evaporated with toluene (10 mL). Itwas then mixed with diisopropylamine tetrazolide (0.36 g, 2.09 mmol) anddried over P₂O₅ under high vacuum at 40° C. overnight. Then it wasdissolved in anhydrous acetonitrile (11 mL) and2-cyanoethyltetraisopropylphosphoramidite (2.66 mL, 8.36 mmol) wasadded.

The reaction mixture was stirred at room temperature under inertatmosphere for 4 hr. Solvent was removed under vacuum. Ethyl acetate (50mL) was added to the residue and washed with 5% NaHCO₃ (30 mL) and brine(30 mL). Organic phase was dried over anhydrous Na₂SO₄ and concentratedto dryness. Residue placed on a flash column and eluted withethylacetate:hexane (60:40) containing a few drops of pyridine to givethe title compound.

EXAMPLE 85 2′-O-Dimethylaminooxyethyl-2,6-diaminopurine RibosidePhosphoramidite

For the incorporation of 2′-O-dimethylaminooxyethyl-2,6-diaminopurineriboside into oligonucleotides, we elected to use the phosphoramidite ofprotected 6-amino-2-fluoropurine riboside. Post-oligo synthesis,concomitant with the deprotection of oligonucleotide protection groups,the 2-fluoro group is displaced with ammonia to give the2,6-diaminopurine riboside analog. Thus, 2,6-diaminopurine riboside isalkylated with dimethylaminooxyethylbromide to afford a mixture of2′-O-dimethylaminooxyethyl-2,6-diaminopurine riboside and the 3′-isomer.Typically after functionalizing the 5′-hydroxyl with DMT to provide5′-O-(4,4′-dimethoxytrityl)-2′-O-dimethylaminooxyethyl-2,6-diaminopurineriboside, the 2′-isomer is resolved chromatographically. Fluorinationvia the Schiemann reaction (Krolikiewicz, K.; Vorbruggen, H. NucleosidesNucleotides, 1994, 13, 673-678) provides2′-O-dimethylaminooxyethyl-6-amino-2-fluoro-purine riboside and standardprotection protocols affords5′-O-(4,4′-dimethoxytrityl)-2′-O-dimethylaminooxyethyl-6-dimethyformamidine-2-fluoropurineriboside. Phosphitylation gives5′-O-(4,4′-dimethoxytrityl)-2′-O-dimethylaminooxyethyl-6-dimethyformamidine-2-fluoropurineriboside-3′-[(2-cyanoethyl)-N,N-diisopropylphosphoramidite].

In the event that amidite cannot be resolved chromatographically fromthe 3′-isomer, the mixture may be treated with adenosine deaminase,which is known to selectively deaminate 2′-O-substituted adenosineanalogs in preference to the 3′-O-isomer, to afford2′-O-dimethylaminooxyethylguanosine.5′-O-(4,4′-dimethoxytrityl)-2′-O-dimethylaminooxyethylguanosine may beconverted to the 2,6-diaminopurine riboside analog by amination of the6-oxo group (Gryaznov, S.; Schultz, R. G. Tetrahedron Lett. 1994,2489-2492). This is then converted to the corresponding amidite bystandard protection methods and protocols for phosphitylation.

EXAMPLE 862′/3′-O-[2-(tert-Butyldimethylsilylhydroxy)ethyl]-2,6-diaminopurineRiboside

2,6-diaminopurine riboside (10 g 35.46 mmol) was dried over P₂O₅ underhigh vacuum. It was suspended in anhydrous DMF (180 mL) and NaH (1.2 g,35.46 mmol, 60% dispersion in mineral oil) was added. The reactionmixture was stirred at ambient temperature at inert atmosphere for 30minutes. To this (2-bromoethoxy)-tert-butyldimethylsilane (12.73 g, 53.2mmol) was added dropwise and the resulting solution was stirred at roomtemperature overnight. DMF was removed under vacuum, residue wasdissolved in ethyl acetate (100 mL) and washed with water (2×70 mL).Ethyl acetate layer was dried over anhydrous MgSO₄ and concentrated todryness. Residue was placed on a flash column and eluted with 5% MeOH inCH₂Cl₂ to get the title mixture of products (6.0711 g, 31% yield). Rf0.49, 0.59, 0.68 (5% MeOH in CH₂Cl₂).

EXAMPLE 87 2′-O-Aminooxyethyl Analogs

Various other 2′-O-aminooxyethyl analogs of nucleoside (for e.g.,2,6-diaminopurine riboside) may be prepared as illustrated above. Thus,alkylation of 2, 6-diamino purine with(2-bromoethoxy)-tert-butyldimethylsilane gives2′-O-tert-butyldimethylsilyloxyethyl-2,6-diaminopurine riboside and the3′-isomer. The desired 2′-O-isomer is resolved by preparation of5′-O-(4,4′-dimethoxytrityl)-2′-O-tert-butyldimethylsilyloxyethyl-2,6-diaminopurineriboside and subjecting the mixture to column chromatography.Deprotection of the silyl group provides5′-O-(4,4′-dimethoxytrityl)-2′-O-hydroxyethyl-2,6-diaminopurine ribosidewhich undergoes a Mitsunobu reaction to give5′-O-(4,4′-dimethoxytrityl)-2′-O-(2-phthalimido-N-oxyethyl)-2,6-diaminopurineriboside. Treatment under Schiemann conditions effects fluorination anddeprotection of the DMT group to yield2′-O-(2-phthalimido-N-oxyethyl)-6-amino-2-fluoropurine riboside.Standard protection conditions provides5′-O-(4,4′-dimethoxytrityl)-2′-O-(2-phthalimido-N-oxyethyl)-6-dimethyformamidine-2-fluoropurineriboside and deprotection of the phthalimido function affords5′-O-(4,4′-dimethoxytrityl)-2′-O-aminooxyethyl-6-dimethyformamidine-2-fluoropurineriboside.

Reductive amination of5′-O-(4,4′-dimethoxytrityl)-2′-O-aminooxyethyl-6-dimethyformamidine-2-fluoropurineriboside with aldehydes or dialdehydes results in cyclic or acyclicdisubstituted 2′-O-aminooxyethyl analogs. Phosphitylation providescyclic or acyclic disubstituted 2′-O-aminooxyethyl analogs asphosphoramidites.

EXAMPLE 88 2′/3′-O (2-tert-Butyldimethylsilylhydroxyethyl)adenosine

Adenosine (10 g, 37.42 mmol) was dried over P₂O₅ under high vacuum. Itwas then suspended in anhydrous DMF (150 mL) and NaH (1.35 g, 56.13mmol) was added. The reaction mixture was stirred at room temperatureunder inert atmosphere for 30 min. Then (2-bromoethyl)-tert-butyldimethylsilane (9.68 mL, 4.4.90 mmol) was addeddropwise and the reaction mixture stirred at room temperature overnight.DMF was removed under vacuum and to the residue dichloromethane (100 mL)was added and washed with water (2×80 mL). Dichloromethane layer wasdried over anhydrous Na₂SO₄ and evaporated to dryness. Residue purifiedby column to get a mixture of the title compounds (4.30 g). Rf 0.49,0.57 (10% MeOH in CH₂Cl₂)

EXAMPLE 89 2′-O-(2-Methyleneiminooxyethyl)thymidine

In a 100 mL round bottom flask, triethylamine-trihydroflouride (8.93 mL,54.8 mmol) was dissolved in anhydrous THF and triethylamine (3.82 mL,27.4 mmol) was added to form a solution. This solution was added to5′-O-tert-butyldiphenylsilyl-2′-O-[(2-formadoximinooxy)ethyl]-5-methyluridine(3.10 g, 5.48 mmol) that had been dried over P₂O₅ under high vacuum andthe reaction mixture was stirred at room temperature overnight. Solventwas removed under vacuum. Residue obtained was placed on a flash columnand eluted with 10% MeOH in CH₂Cl₂ to give the title compound as whitefoam (1.35 g, 75% yield). Rf 0.45 (5% MeOH in CH₂Cl₂). MS (FAB^(⊕)) m/e330 (M+He^(⊕)), 352 (M+Na^(⊕)).

EXAMPLE 90 5′-O-Dimethoxytrityl-2′-O-(2-methyleneiminooxyethyl)thymidine

2′-O-(2-methyleneiminooxyethyl) thymidine (0.64 g, 1.95 mmol) was driedover P₂O₅ under high vacuum overnight. It was then co-evaporated withanhydrous pyridine (5 mL). Residue dissolved in anhydrous pyridine (4.43mL) and dimethoxytrityl chloride (0.79 g, 2.34 mmol), and4-dimethylaminopyridine (23.8 mg, 0.2 mmol) was added. Reaction mixturewas stirred under inert atmosphere at ambient temperature for 4 hrs.Solvent was removed under vacuum, the residue purified by column andeluted with 5% MeOH in CH₂Cl₂ containing a few drops of pyridine to givethe title compound as a foam (1.09 g, 88% yield). Rf 0.4 (5% MeOH inCH₂Cl₂). MS (Electrospray⁻) m/e 630 (M−H^(⊕)).

EXAMPLE 915′-O-Dimethoxytrityl-2′-O-(2-methyleneiminooxyethyl)thymidine-3′-O-phosphoramidite

5′-O-dimethoxytrityl-2′-O-(2-methyleneiminooxyethyl)thymidine (0.87 g,1.34 mmol) was co-evaporated with toluene (10 mL). Residue was thenmixed with diisopropylamine tetrazolide (0.23 g, 1.34 mmol) and driedover P₂O₅ under high vacuum overnight. It was then flushed with argon.Anhydrous acetonitrile (6.7 mL) was added to get a clear solution. Tothis solution 2-cyanoethyl tetraisopropylphosphorodiamidites (1.7 mL,5.36 mmol) was added and the reaction mixture was stirred at roomtemperature for 6 hr. under inert atmosphere. Solvent was removed undervacuum, the residue was diluted with ethyl acetate (40 mL), and washedwith 5% NaHCO₃ (20 mL) and brine (20 mL). Ethyl acetate layer was driedover anhydrous Na₂SO₄ and concentrated to dryness. Residue placed on aflash column and eluted with ethyl acetate: hexane (60:40) to give thetitle compound (1.92 g, 80% yield). Rf 0.34 (ethyl acetate:hexane,60:40). ³¹P NMR (CDCl₃) δ 150.76 ppm, MS (Electrospray⁻) m/e 830(M−H^(⊕)).

EXAMPLE 92 Attachment of a Nucleoside to Solid Support General Procedure

5′-O-DMT-2′-O-(dimethylaminooxyethyl)-5-methyluridine (200 mg, 0.31mmol) was mixed with DMAP (19 mg, 16 mmol), succinic anhydride (47 mg,0.47 mmol), triethylamine (86 mL, 0.62 mmol) and dichloromethane (0.8mL) and stirred for 4 hr. The mixture was diluted with CH₂Cl₂ (50 mL)and the CH₂Cl₂ layer was washed first with ice cold 10% aqueous citricacid and then with water. The organic phase was concentrated to drynessto give the nucleoside bound to the solid support through a succinyllinker at the 3′-O— group. The solid support bound material wasdissolved in anhydrous acetonitrile (23 mL). To this DMAP (37 mg, 0.3mmol), and 2′,2′-dithiobis(5-nitropyridine) (103 mg, 0.33 mmol) wereadded. The solution was stirred for 5 min. To this was addedtriphenylphosphine (78.69 mg, 0.3 mmol) in anhydrous acetonitrile (3mL). The solution was stirred for 10 min. and then CPG was added to it.The slurry was then shaken for 2 hr. It was then filtered, washed withacetonitrile and CH₂Cl₂. The functionalized CPG was dried and cappedwith capping solution to give the solid support bound 2′-O-modifiednucleoside. Loading capacity was determined (58.3 μmol/g).

EXAMPLE 93 Synthesis of Aminooxy Derivatives: Alternative Procedure

5′-O-dimethoxytrityl-2′-O-hydroxyethyl thymidine is converted to the2′-O-(O-tosyl)hydroxyethyl derivative by treatment with 1 equivalent ofp-toluenesulfonyl chloride-pyridine followed by standard work-up. Thetosylate is subsequently treated with several amino-hydroxy compounds toact as nucleophils in displacing tosylate to yield a series of oxy-aminocompounds. The reaction is facilitated by preforming the anion from theamino alcohol or hydroxylamine derivative by the use of sodium hydrideunder anhydrous conditions.

EXAMPLE 94 Oligomer Synthesis

Solid support bound 2′-O-methyl-5-methyl-5′-O-DMT-uridine attached tosolid support through the 3′-O— is purchased from ChemGenes. The5′-O-DMT blocking group is removed as per standard protocols. The solidsupport bound material is coupled via oxidative phosphorylation to theproduct of Example 27 to give a modified dimer in a protected form. Themodified dimer can be elongated by addition of nucleosides and ornucleotides. Additional modified dimers are added by coupling theproduct of Example 28 followed by the coupling of the product of Example27. The TBDPS groups are removed by treatment with F⁻.

EXAMPLE 95 General Procedure for the Synthesis of Oligonucleotides andOligonucleotide Analogs

The synthesis of oligonucleotides and oligonuclectide analogs was bystandard automated synthesis using starndard reagents and methods.Phosphoramidites (0.1 M) in anhydrous acetonitrile were employed in 1μmol scale syntheses following standard protocol for DNA synthesis. Thecoupling of modified dimers such as the MMI dimer3′-de(oxyphosphinico)-3′-(methyleneimino)-5′-DMT-2′-O-acetyl-5-methyluridylyl(3>5)-2′-O-methyl-5-methyluridine-3′-phosphoramidite(TT¹ above), was allowed to proceed for 15 minutes on the synthesizerand the process was repeated three times.(1S)-(+)-10-(camphorsulfonyl)oxaziridine was used as the oxidizer.Oligonucleotide analogs were synthesized as 5′-O-DMT derivatives. Theywere cleaved from solid support, base-deprotected and 2′-O-deacetylatedby incubation in 30% aqueous ammonia overnight at 55° C. The resultingcrude material was purified by reverse-phase HPLC on C-18 column with 50mM triethylammonium acetate and acetonitrile as eluents utilizing agradient from 5 to 60% acetonitrile in 60 minutes and a flow rate of 2.5mL/minute. Cleavage of 5′-O-DMT in 80% aqueous AcOH at room temperaturein 0.5 hour was followed by size-exclusion chromatography on G-25column. The characterization and purity of the isolated oligonucleotideanalogs was determined by HPLC, CE and ES MS (See Table).

EXAMPLE 96 Enhanced Binding Affinity of Compounds of the Invention

To illustrate the enhanced affinity for complementary RNA shown bycompounds of the invention, oligonucleotide 30 analogs were synthesizedhaving from 1 to 5 modified dimers incorporated therrein. Backbonelinkages of the oligonucleotide analogs assayed were phosphodiesterexcept for the linkages in each individual modified dimers which wereMMI (the dimer structures are shown below). Dimers that are joined toother dimers in a sequence were joined by phosphodiester linkages. A DNAsequence was also prepared for each of the 3 sequences being used in thestudy. The thermal melt of each of the oligonucleotide analogs shownbelow was measured against RNA, as was the corresponding DNA sequence.Comparison of the T_(m)'s of each oligonucleotide analog with itscorresponding DNA sequence gave the ΔT_(m) values below in Table I.

TABLE I SEQ ID NO: Sequence ΔT_(m)/mod 1 CTC GTA CC TT ¹ TC CGG TCC 2.262 CTC GTA CC TT ² TC CGG TCC 1.85 3 CTC GTA CC TT ³ TC CGG TCC 1.51 4CTC GTA C TT ¹ TT ¹ C CGG TCC 3.19 5 CTC GTA C TT ² TT ² C CGG TCC 2.786 CTC GTA C TT ³ TT ³ C CGG TCC −0.23 7 GCG TT ¹ TT ¹ TT ¹ TT ¹ TT ¹ GCG 3.83 8 GCG TT ² TT ² TT ² TT ² TT ² GC G 3.80 9 GCG TT ³ TT ³ TT ³ TT³ TT ³ GC G 0.13 TT ¹

TT ²

TT ³

The highest ΔT_(m) values were seen with oligonucleotide analogsincorporating modified dimers having the combination of an unmodifiedribose moiety in the 5′nucleoside arid a 2′-O—CH₃ group attached to theribose moiety in the 3′nucleoside (TT¹). In comparison, the2′,2¹¹-O-bis-methoxy modified dimer (TT²) showed an increased T_(m)compared to DNA, but not as high as the TT¹dimer. The ribose unmodifieddimer (TT³) showed a reduced affinity compared to its complementary DNAanalog.

PROCEDURE 1 Nuclease Resistance

A. Evaluation of the Resistance of Oligonucleotide Analogs to Serum andCytoplasmic Nucleases.

Oligonucleotides including oligonucleotide analogs of the invention canbe assessed for their resistance to serum nucleases by incubation inmedia containing various concentrations of fetal calf serum or adulthuman serum. Labeled oligonucleotides are incubated for various times,treated with protease K and then analyzed by gel electrophoresis on 20%polyacrylamide-urea denaturing gels and subsequent autoradiography.Autoradiograms are quantitated by laser densitometry. Based upon thelocation of the modifications and the known length of theoligonucleotide it is possible to determine the effect on nucleasedegradation by the particular modification. For the cytoplasmicnucleases, a HL60 cell line is used. A post-mitochondrial supernatant isprepared by differential centrifugation and the labeled oligonucleotidesare incubated in this supernatant for various times. Following theincubation, oligonucleotides are assessed for degradation as outlinedabove for serum nucleolytic degradation. Autoradiography results arequantitated for comparison of the unmodified and modifiedoligonucleotides. As a control, unsubstituted phosphodiesteroligonucleotide have been found to be 50% degraded within 1 hour, and100% degraded within 20 hours.

B. Evaluation of the Resistance of Oligonucleotide Analogs to SpecificEndo- and Exonucleases

Evaluation of the resistance of naturaly occurring and non-naturallyoccurring oligonucleotides including oligonucleotide analogs of theinvention to specific nucleases (i.e., endonucleases, 3′,5′-exo-, and5′,3′-exonucleases) is done to determine the exact effect ondegradation. Oligonucleotide analogs are incubated in defined reactionbuffers specific for various selected nucleases. Following treatment ofthe products with protease K, urea is added and analysis on 20%polyacrylamide gels containing urea is done. Gel products are visualizedby staining using Stains All (Sigma Chemical Co.). Laser densitometry isused to quantitate the extend of degradation. The effects of themodifications are determined for specific nucleases and compared withthe results obtained from the serum and cytoplasmic systems.

It is intended that each of the patents, applications, printedpublications, and other published documents mentioned or referred to inthis specification be herein incorporated by reference in theirentirety.

Those skilled in the art will appreciate that numerous changes andmodifications may be made to the preferred embodiments of the inventionand that such changes and modifications may be made without departingfrom the spirit of the invention. It is therefore intended that theappended claims cover all such equivalent variations as fall within thetrue spirit and scope of the invention.

9 1 18 DNA Artificial Sequence Oligonucleotide 1 ctcgtacctt tccggtcc 182 18 DNA Artificial Sequence Oligonucleotide 2 ctcgtacctt tccggtcc 18 318 DNA Artificial Sequence Oligonucleotide 3 ctcgtacctt tccggtcc 18 4 18DNA Artificial Sequence Oligonucleotide 4 ctcgtacttt tccggtcc 18 5 18DNA Artificial Sequence Oligonucleotide 5 ctcgtacttt tccggtcc 18 6 18DNA Artificial Sequence Oligonucleotide 6 ctcgtacttt tccggtcc 18 7 16DNA Artificial Sequence Oligonucleotide 7 gcgttttttt tttgcg 16 8 16 DNAArtificial Sequence Oligonucleotide 8 gcgttttttt tttgcg 16 9 16 DNAArtificial Sequence Oligonucleotide 9 gcgttttttt tttgcg 16

What is claimed is:
 1. A compound having Formula:

wherein: Z is a covalent intersugar linkage selected from the groupconsisting of 3′-CH₂—NH—O—, 3′-CH₂—N(CH₃)—O—, 3′-amino phosphoramidate,and 3′-amino phosphorothioamidate; each T₁ and T₂ is, independently,—OH, —OR₁, —CH₂R₁, —NH(R₁), —SH, —SR₁, or a blocked hydroxyl; R₁ isC₁-C₁₂ alkyl; B_(X) is a heterocyclic base; X is F, —O—R, —S—R or—NR(R₂); R is alkyl, or a ring system having from about 4 to about 7carbon atoms or having from about 3 to about 6 carbon atoms and 1 or 2hetero atoms wherein said hetero atoms are selected from oxygen,nitrogen and sulfur and wherein said ring system is aliphatic,unsaturated aliphatic, aromatic or heterocyclic; and wherein anyavailable hydrogen atom of said ring system is each replaceable with analkoxy, alkylamino, urea or alkylurea group; or R has one of theformulas:

 wherein Q is O, S or NR₂; m is from 1 to 10; y is from 0 to 10; E isN(R₂)(R₃), N═C(R₂)(R₃), C₁-C₁₀ alkyl, or C₁-C₁₀ substituted alkylwherein said substituent is N(R₂)(R₃); and each R₂ and R₃ is,independently, H, C₁-C₁₀ alkyl, alkylthioalkyl, a nitrogen protectinggroup, or R₂ and R₃, together, are a nitrogen protecting group orwherein R₂ and R₃ are joined in a ring structure that can include atleast one heteroatom selected from N and O.
 2. The compound of claim 1wherein X is —O—R.
 3. The compound of claim 2 wherein R is —CH₃.
 4. Thecompound of claim 2 wherein R is —CH₂—CH₂—O—CH₃.
 5. The compound ofclaim 1 wherein Z is —CH₂—N(CH₃)—O—.
 6. The compound of claim 2 whereinR is —CH₂—CH₂—O—N(CH₃)₂.
 7. An oligonucleotide analog comprising atleast one moiety having Formula:

wherein each Z is a covalent intersugar linkage selected from the groupconsisting of 3′-CH₂—N—H—O—, 3′-CH₂—N(CH₃)—O—, 3′-amino phosphoramidate,and 3′-amino phosphorothioamidate; T₃ is a nucleotide other than aribonucleotide, a nucleoside other than a ribonucleoside, a hydroxyl, ablocked hydroxyl, or an oligonucleotide wherein the 3′-terminalnucleotide of said oligonucleotide is not a ribonucleotide; T₄ is anucleotide, a nucleoside, an oligonucleotide, a hydroxyl or a blockedhydroxyl; with the proviso that at least one of said T₃ and T₄ is not ahydroxyl, or blocked hydroxyl; B_(X) is a heterocyclic base; each X isF, —O—R, —S—R or —NR(R₂); R is alkyl, or a ring system having from about4 to about 7 carbon atoms or having from about 3 to about 6 carbon atomsand 1 or 2 hetero atoms wherein said hetero atoms are selected fromoxygen, nitrogen and sulfur and wherein said ring system is aliphatic,unsaturated aliphatic, aromatic or heterocyclic; and wherein anyavailable hydrogen atom of said ring system is each replaceable with analkoxy, alkylamino, urea or alkylurea group; or R has one of theformulas:

 wherein Q is O, S or NR₂; m is from 1 to 10; y is from 1 to 10; E isN(R₂)(R₃), N═C(R₂)(R₃), C₁-C₁₀ alkyl, or C₁-C₁₀ substituted alkylwherein said substituent is N(R₂)(R₃); each R₂ and R₃ is, independently,H, C₁-C₁₀ alkyl, alkylthioalkyl, a nitrogen protecting group, or R₂ andR₃, together, are a nitrogen protecting group or wherein R₂ and R₃ arejoined in a ring structure that can include at least one heteroatomselected from N and O; and R₁ is H or C₁-C₁₂ alkyl.
 8. Theoligonucleotide analog of claim 7 wherein at least one X is —O—R.
 9. Theoligonucleotide analog of claim 8 wherein R is —CH₃.
 10. Theoligonucleotide analog of claim 8 wherein R is —CH₂—CH₂—O—CH₃.
 11. Theoligonucleotide analog of claim 7 having a length of from 1 to 200subunits.
 12. The oligonucleotide analog of claim 7 having a length offrom 10 to 25 subunits.
 13. The oligonucleotide analog of claim 7 havinga length of from 12 to 20 subunits.
 14. The compound of claim 7 whereinZ is —CH₂—N(CH₃)—O—.
 15. The oligonucleotide analog of claim 7 wherein Ris —CH₂—CH₂—O—N(CH₃)₂.
 16. A compound comprising a moiety of Formula:

wherein: Z is a covalent intersugar linkage selected from the groupconsisting of 3′-CH₂—NH—O—, 3′-CH₂—N(CH₃)—O—, 3′-amino phosphoramidate,and 3′-amino phosphorothioamidate; B_(X) is a heterocyclic base; X is F,—O—R, —S—R or —NR(R₂); R is alkyl, or a ring system having from about 4to about 7 carbon atoms or having from about 3 to about 6 carbon atomsand 1 or 2 hetero atoms wherein said hetero atoms are selected fromoxygen, nitrogen and sulfur and wherein said ring system is aliphatic,unsaturated aliphatic, aromatic or heterocyclic; and wherein anyavailable hydrogen atom of said ring system is each replaceable with analkoxy, alkylamino, urea or alkylurea group; or R has one of theformulas:

 wherein Q is O, S or NR₂; m is from 1 to 10; y is from 0 to 10; E isN(R₂)(R₃), N═C(R₂)(R₃), C₁-C₁₀ alkyl, or C₁-C₁₀ substituted alkylwherein said substituent is N(R₂)(R₃); each R₂ and R₃ is, independently,H, C₁-C₁₀ alkyl, alkylthioalkyl, a nitrogen protecting group, or R₂ andR₃, together, are a nitrogen protecting group or wherein R₂ and R₃ arejoined in a ring structure that can include at least one heteroatomselected from N and O; T₃ is a nucleotide, a nucleoside, anoligonucleotide, a hydroxyl or a blocked hydroxyl, wherein saidnucleotide is not a ribonucleotide, and said nucleoside is not aribonucleoside, and wherein the 3′-terminal nucleotide of saidoligonucleotide is not a ribonucleotide; and R₁ is H or C₁-C₁₂ alkyl.17. The compound of claim 16 wherein X is —O—R.
 18. The compound ofclaim 17 wherein R is —CH₃.
 19. The compound of claim 17 wherein R is—CH₂—CH₂—O—CH₃.
 20. The compound of claim 16 wherein Z is—CH₂—N(CH₃)—O—.
 21. The compound of claim 17 wherein R is—CH₂—CH₂—O—N(CH₃)₂.